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1

Applications of laser-induced gratings to spectroscopy and dynamics  

SciTech Connect

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

Rohlfing, E.A. [Sandia National Laboratories, Livermore, CA (United States)

1993-12-01

2

Study of laser induced plasma grating dynamics in gases  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

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 Transient Grating Analysis of Dynamics of Interaction between Sensory Rhodopsin II D75N and the HtrII Transducer  

PubMed Central

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

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

2007-01-01

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

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

7

Polarization-dependent single-beam laser-induced grating-like effects on titanium films  

Microsoft Academic Search

In this paper we present results on polarization-dependent laser-induced effects on titanium (Ti) thin films. We irradiated the titanium films, in ambient air, using a nanosecond Nd:YAG laser (532nm, 9ns pulse duration, 10Hz). Using a series of pulses of fluence well below the ablation threshold, it was possible to form grating-like structures, whose grooves run parallel to the linear polarization

Santiago Camacho-López; Rodger Evans; Luis Escobar-Alarcón; Miguel A. Camacho-López; Marco A. Camacho-López

2008-01-01

8

Femtosecond laser induced fiber Bragg gratings for harsh environment sensing applications  

NASA Astrophysics Data System (ADS)

Fiber Bragg grating sensors have been developed beyond a laboratory curiosity to become a mainstream sensing technology because of their small size, passive nature, immunity to electromagnetic interference, and capability to simultaneously measure multiple physical parameters such as temperature, strain and pressure. Recently, high temperature stable gratings based on regeneration techniques and femtosecond infrared laser processing have shown promise for use in extreme environments such as high temperature, pressure or ionizing radiation. Such gratings are ideally suited for energy production applications where there is a requirement for advanced energy system instrumentation and controls that are operable in harsh environments. This presentation will give a review of some of the more recent developments of femtosecond laser induced fiber Bragg gratings.

Mihailov, S. J.; Grobnic, D.; Walker, R. B.; Lu, P.; Ding, H.

2014-09-01

9

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

10

November 1, 1994 / Vol. 19, No. 21 / OPTICS LETTERS 1681 Laser-induced thermal grating effects in flames  

E-print Network

commonlyused in resonant four-wavemixing and laser-induced grating spectroscopy. The presence of thermal is tuned to a resonant spectroscopictransition, a density modulation results from the localized absorption the spectral response by detuning E2 from E1 and E3, which are maintained at the line center of the Q21

Zare, Richard N.

11

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

E-print Network

Ultrafast dynamics of the laser-induced solid-to-liquid phase transition in aluminum A thesis dynamics of the laser-induced solid-to-liquid phase transition in aluminum Eric Mazur Maria Kandyla Abstract This dissertation reports the ultrafast dynamics of aluminum during the solid-to- liquid phase

Mazur, Eric

12

Molecular Dynamics Simulations of Laser Induced Incandescence Dr. Adri van Duin  

E-print Network

Molecular Dynamics Simulations of Laser Induced Incandescence (LII) Dr. Adri van Duin Associate process we performed reactive molecular dynamics (MD) simulations, using a ReaxFF C/H/O parameter set. Molecular Dynamics Simulations of Laser-Induced Incandescence of Soot Using an Extended ReaxFF Reactive

Bjørnstad, Ottar Nordal

13

Dynamic holographic gratings  

NASA Astrophysics Data System (ADS)

The work presented in this thesis is divided into two related areas. The first area of research was a study of photoanisotropic materials to record dynamic gratings. The second area was a study of stimulated diffusion backscattering in photorefractive crystals. The two areas are related by the fact that in the two cases we studied dynamic gratings. We studied reversible photochemical mechanisms using dye molecules suspended in polymer hosts that could record dynamic holograms. The self-developing refractive index changes in dye-doped or dye-attached polymer materials, in particularly azo-dye-doped polymer systems make them promising candidates for many applications (because of the large photoinduced birefringence). The mechanism of photoanisotropic recording in azo-dye-doped polymer materials is based on orientationally dependent photoisomerization of dye molecules that may be macroscopically described in terms of photoinduced linear dichroism and linear birefringence. We proposed a technique for the fabrication of thick photosensitized polymer materials for real-time (self- developing) holographic applications. Cross modulation experiments to study the photoinduced dichroism are then described and the discussion of photophysical mechanisms involved is given. We used azo-dye doped polymer materials to record thin and thick holograms (scalar and vector). We theoretically and experimentally demonstrated that one could successfully store (using a linearly and an elliptically polarized beams) and reconstruct an elliptical polarization state of light using photoanisotropic materials, even if a plane polarized reference beam is used for the recording and readout. Using photoanisotropic materials, we demonstrated experimentally and theoretically that macroscopic optical chirality may be generated in such systems with a proper choice of excitation beam polarization state. Linear diffraction gratings, that provide strongly asymmetric diffraction without surface modulation were also created and studied. Asymmetric diffraction may be achieved using blazed gratings. But in our case the spatial phase shift of the refractive index grating relative to the absorption grating is the origin of asymmetric behaviour. Experimental results made with thin mixed phase and absorption gratings in azo-dye-doped polymer films are in agreement with our theoretical results. In the second part of the thesis we analysed the stimulated diffusion backscattering (SDS) in photorefractive crystals based on the advantages of the reflection photorefractive gratings. The material research, which is the most acute direction, was studied. We believe that optimal crystal (its processing procedure and doping density) is still unknown even for visible range. We discussed the general analysis of the stimulated diffusion backscattering. We studied the relevant parameters for the sample, which demonstrated the most interesting stimulated diffusion backscattering response: measurements of gain, reflectivity, response rate, dark conductivity and grating decay. We clarified the principal possibilities to obtain self-phase conjugation at backward SDS in steady-state conditions. We also made the comparison of sensitivities of different geometries with respect to pump energy. Finally, we experimentally studied double-phase-conjugation geometry at double-loop reflection gratings.

Birabassov, Rouslan

2001-10-01

14

Generation of inhomogeneous bulk plane acoustic modes by laser-induced thermoelastic grating near mechanically free surface  

SciTech Connect

The detailed theoretical description of how picosecond plane shear acoustic transients can be excited by ultrafast lasers in isotropic media is presented. The processes leading to excitation of inhomogeneous plane bulk compression/dilatation (c/d) and shear acoustic modes by transient laser interference pattern at a mechanically free surface of an elastically isotropic medium are analyzed. Both pure modes are dispersive. The modes can be evanescent or propagating. The mechanical displacement vector in both propagating modes is oriented obliquely to the mode propagation direction. Consequently the c/d mode is not purely longitudinal and shear mode is not purely transversal. Each of the propagating modes has a plane wave front parallel to the surface and the amplitude harmonically modulated along the surface. Inhomogeneous shear acoustic mode cannot be generated in isotropic medium by thermal expansion and is excited by mode conversion of laser-generated inhomogeneous c/d acoustic mode incident on the surface. The spectral transformation function of the laser radiation conversion into shear modes has one of its maxima at a frequency corresponding to transmission from laser-induced generation of propagating to laser-induced generation of evanescent c/d modes. At this particular frequency the shear waves are due to their Cherenkov emission by bulk longitudinal acoustic waves skimming along the laser-irradiated surface, which are generated by laser-induced gratings synchronously. There exists an interval of frequencies where only shear acoustic modes are launched in the material by laser-induced grating, while c/d modes generated by thermoelastic optoacoustic conversion are evanescent. Propagating picosecond plane shear acoustic fronts excited by interference pattern of fs-ps laser pulses can be applied for the determination of the shear rigidity by optoacoustic echoes diagnostics of thin films and coatings. Theoretical predictions are correlated with available results of experiments and of numerical modeling.

Gusev, Vitalyi [LPEC, UMR-CNRS 6087, ENSIM, PRES UNAM, Universite du Maine, 72085 Le Mans (France)

2010-06-15

15

Quantum dynamics of laser-induced desorption from metal and semiconductor surfaces, and related phenomena  

Microsoft Academic Search

Recent progress towards a quantum theory of laser-induced desorption and related phenomena is reviewed, for specific examples. These comprise the photodesorption of NO from Pt(111), the scanning tunnelling microscope and laser-induced desorption and switching of H at Si(100), and the electron stimulated desorption and dissociation of CO at Ru(0001). The theoretical methods used for nuclear dynamics range from open-system density

Peter Saalfrank; Mathias Nest; Ivan Andrianov; Tillmann Klamroth; Dominik Kröner; Stephanie Beyvers

2006-01-01

16

A Femtosecond-Laser-Induced Fiber Bragg Grating with Supermode Resonances for Sensing Applications  

NASA Astrophysics Data System (ADS)

A Bragg grating is inscribed into the cladding of an all-solid photonic bandgap fiber by use of side femtosecond illumination. Multimode resonances are observed, with calculations resulting from guided supermodes in the cladding by the phase matching condition. All supermode resonances show nearly the same sensitivity to strain and temperature, about 0.98 pm/?? and 12.78 pm/°C, respectively, while their resonant wavelengths are insensitive to bend. An annealing test shows that this grating can endure temperatures higher than 1100°C where it can still keep high reflectivity and good repeatability. Such a Bragg grating could have potential applications in fiber sensors for strain and temperature measurements, with low cross-sensitivity to bend or an external refractive index, especially in harsh environments.

Liu, Ning-Liang; Liu, Shu-Hui; Lu, Pei-Xiang

2014-09-01

17

Laser induced temperature jump investigations of fast protein folding dynamics  

NASA Astrophysics Data System (ADS)

Protein folding has a large parameter space, diverse mechanism, and multipath kinetics. However, there are some common features many proteins share in their folding processes: all seem to fold at the rates much faster than the random conformation search, and all fold into the structures which have the highly regular motifs like alpha-helices, beta-sheets and turns. Understanding how fast proteins can fold is one of the central issues in solving the protein folding problem. Ultrafast folding kinetics had not been accessible until a few sub-millisecond probes were invented and applied lately. We constructed a laser induced temperature jump spectrometer which is a great utility in identifying the local structure and tertiary contact formation of proteins on the time scale from 10 -8 to 10-3 s with time resolution of 10 -9 s. With this spectrometer we studied the fast folding mini-protein, TrpCage and a few short stable beta-hairpins, the TrpZip series. Studying TrpCage was a major breakthrough it was a pioneer protein model which brought experiment and simulation very close: its structures measured by NMR and predicted by the molecular dynamics were amazingly alike. Our kinetic results showed that it folds in 4 mus at room temperature which turned out to be the fastest ever known for protein-like molecules. Also this folding time constant is consistent with what was later on simulated by distributed computation. TrpZips are among the smallest and stablest polypeptide chains which form secondary structures. They are slightly different from each other based on structural stability and by forming various types of beta-hairpins which are the minimum units of beta tertiary structure. The beta-hairpins form in the time range of 1--10 mus that confirms the theory that loop formation is controlled by the diffusion process (˜mus). We also investigated the kinetics of the protein chain collapse, a very controversial problem. By comparing the collapse of the foldable 104-residue protein cytochrome c and its unfoldable fragments F1-65 and F1-80, we concluded that the collapse of the protein molecule is not significantly different from those of unfoldable peptide chains. Burial of hydrophobic core and the presence of the interactions among chain residues and the interactions between amino acids and solvent molecules limit the collapse rate of a polypeptide chain on the time scale of the order of ten microseconds.

Qiu, Linlin

18

BRIEF REPORT Dynamics of ArF Excimer Laser-induced  

E-print Network

Organization and NanoMed, Jerusalem, Israel Background and Objective: Cavitation bubbles have been shownBRIEF REPORT Dynamics of ArF Excimer Laser-induced Cavitation Bubbles in Gel Surrounded by a Liquid. In the present work we investigate the dynamics of cavitation bubbles inside a gelatin gel in a saline

Palanker, Daniel

19

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. PMID:21339990

Tang, Hong; Li, Hongjian; Dou, Yusheng

2011-01-01

20

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

PubMed

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

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

2014-12-11

21

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

22

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

E-print Network

Time-resolved diffraction profiles and atomic dynamics in short-pulse laser-induced structural on the atomic-level structural rearrangements available from the simulations to the diffraction spectra measured of the irradiated surface and provides limited direct information on atomic structural rearrangements. Recent

Zhigilei, Leonid V.

23

Dynamics of femtosecond laser-induced melting of silver  

NASA Astrophysics Data System (ADS)

We use optical third-harmonic generation to measure the melting dynamics of silver following femtosecond laser excitation. The dynamics reveals an unusual two-step process that is associated with the extreme electronic temperatures and very short time and length scales. In the first, which lasts a few picoseconds, the electron and phonon systems begin to equilibrate, and a thin surface layer undergoes melting. Heat conduction during this period is strongly suppressed by electron scattering from d -band excitations. In the second stage, the surface region remains above the melting temperature for a surprisingly long time, 20-30 ps, with the melt front propagating into the bulk at a velocity of ?350ms-1 . In this stage, the electron and phonon systems again fall out of equilibrium and conduction of heat away from the surface region is now limited by the weak electron-phonon (e-p) coupling. From our model calculation, we propose that the melt depths in noble metals irradiated by femtosecond lasers are limited to thicknesses on the order of two to three times of the optical-absorption depth of the light.

Chan, Wai-Lun; Averback, Robert S.; Cahill, David G.; Lagoutchev, Alexei

2008-12-01

24

Laser-induced magnetization dynamics in a cobalt/garnet heterostructure  

NASA Astrophysics Data System (ADS)

We report on magnetization dynamics triggered in a Co/garnet heterostructure by femtosecond laser pulses. Although laser excitation of a bare Co-doped yttrium iron garnet leads to magnetization precession, the phase of which strongly depends on the linear polarization of the light pulses, the deposition of an ultrathin Co layer on a top of a garnet film results in substantial changes of the laser-induced dynamics. The precession in the garnet is shown to lose its sensitivity to the polarization. Instead, light triggers polarization insensitive precession in both the magnetostatically coupled Co layer and the garnet film at two distinct frequencies typical for Co and garnet layers.

Pashkevich, M.; Stupakiewicz, A.; Kimel, A.; Kirilyuk, A.; Stognij, A.; Novitskii, N.; Maziewski, A.; Rasing, Th.

2014-01-01

25

Laser-induced magnetization dynamics of lanthanide-doped permalloy thin films.  

PubMed

We investigate the effect of Ho, Dy, Tb, and Gd impurities on the femtosecond laser-induced magnetization dynamics of thin Permalloy films using the time-resolved magneto-optical Kerr effect. Varying the amount of Ho, Dy, Tb content from 0% to 8%, we observe a gradual change of the characteristic demagnetization time constant from approximately 60 to approximately 150 fs. In contrast, Gd concentrations up to 15% do not influence the time scale of the initial photoinduced magnetization loss. We propose a demagnetization mechanism that relies on strong magnetic inertia of the rare-earth dopant which stabilizes the ferrimagnetic ordering and thereby delays the demagnetization. PMID:19392235

Radu, I; Woltersdorf, G; Kiessling, M; Melnikov, A; Bovensiepen, U; Thiele, J-U; Back, C H

2009-03-20

26

Femtosecond diffraction dynamics of laser-induced periodic surface structures on fused silica  

NASA Astrophysics Data System (ADS)

The formation of laser-induced periodic surface structures (LIPSS) on fused silica upon irradiation with linearly polarized fs-laser pulses (50 fs pulse duration, 800 nm center wavelength) is studied experimentally using a transillumination femtosecond time-resolved (0.1 ps-1 ns) pump-probe diffraction approach. This allows to reveal the generation dynamics of near-wavelength-sized LIPSS showing a transient diffraction at specific spatial frequencies even before a corresponding permanent surface relief was observed. The results confirm that the ultrafast energy deposition to the materials surface plays a key role and triggers subsequent physical mechanisms such as carrier scattering into self-trapped excitons.

Höhm, S.; Rosenfeld, A.; Krüger, J.; Bonse, J.

2013-02-01

27

Effects of an absorptive coating on the dynamics of underwater laser-induced shock process  

NASA Astrophysics Data System (ADS)

The effects of an absorptive coating on the dynamics of underwater laser-induced shock process have been observed from the end of laser pulse to hundreds of microseconds after irradiation by time-resolved imaging techniques. A laser pulse of 13 ns at 1,064 nm was focused by a 40-mm focal length lens onto the surface of epoxy-resin blocks immersed in water to induce the shock process in the confining regime. A custom-designed time-resolved photoelasticity imaging technique and a high-speed laser stroboscopic videography technique in photoelasticity mode were used to analyze the evolution of shock waves in the water phase, the strength of stress waves in the solid phase, the oscillation of cavitation bubbles, and the generation of bubble-collapse-induced shock waves. We showed that black paint coating enhances the strength of laser-induced stress wave inside the solid, drives faster shock waves traveling in the water phase, and produces higher-energy cavitation bubbles. We propose that even at power densities of 1 GW/cm2 and above, an absorptive coating can intensify the shock process by enhancing the absorption of laser energy by plasma.

Nguyen, Thao Thi Phuong; Tanabe, Rie; Ito, Yoshiro

2014-09-01

28

Investigating the dynamics of laser induced sparks in atmospheric helium using Rayleigh and Thomson scattering  

NASA Astrophysics Data System (ADS)

We have used optical Rayleigh and Thomson scattering to investigate the expansion dynamics of laser induced plasma in atmospheric helium and to map its electron parameters both in time and space. The plasma is created using 9 ns duration, 140 mJ pulses from a Nd:YAG laser operating at 1064 nm, focused with a 10 cm focal length lens, and probed with 7 ns, 80 mJ, and 532 nm Nd:YAG laser pulses. Between 0.4 ?s and 22.5 ?s after breakdown, the electron density decreases from 3.3 × 1017 cm-3 to 9 × 1013 cm-3, while the temperature drops from 3.2 eV to 0.1 eV. Spatially resolved Thomson scattering data recorded up to 17.5 ?s reveal that during this time the laser induced plasma expands at a rate given by R ˜ t0.4 consistent with a non-radiative spherical blast wave. This data also indicate the development of a toroidal structure in the lateral profile of both electron temperature and density. Rayleigh scattering data show that the gas density decreases in the center of the expanding plasma with a central scattering peak reemerging after about 12 ?s. We have utilized a zero dimensional kinetic global model to identify the dominant particle species versus delay time and this indicates that metastable helium and the He2+ molecular ion play an important role.

Nedanovska, E.; Nersisyan, G.; Morgan, T. J.; Hüwel, L.; Murakami, T.; Lewis, C. L. S.; Riley, D.; Graham, W. G.

2015-01-01

29

Dynamics of laser-induced magnetization in Ce-doped yttrium aluminum garnet  

SciTech Connect

Circularly polarized short laser pulse induces nonequilibrium population of spin levels in the excited state of Ce{sup 3+}-ion embedded in yttrium aluminium garnet crystal and, consequently, the magnetization of the crystal associated with spin polarization. Dynamic behavior of laser-induced magnetization is studied as a function of the external magnetic field. It reveals spin oscillations attributed to the effect of hyperfine magnetic field produced by {sup 27}Al nuclei on the Ce{sup 3+} spin. A simple theoretical model explaining spin oscillations is presented. It shows that circularly polarized light induces spin coherence at the transition between Zeeman sublevels of Ce{sup 3+} ion in the lowest 5d state. Temporal shape of laser-induced magnetization signal reveals the following parameters of this state: (1) the spin-lattice relaxation constant is {approx_equal}2x10{sup 7} s{sup -1}, (2) inhomogeneous spin dephasing time is {approx_equal}4 ns, and (3) the g tensor of the state seems to be isotropic with the g factor being in the range 0.7-0.9. In addition, the width of the local hyperfine field distribution is {approx_equal}40 G.

Kolesov, Roman [Department of Physics and Institute for Quantum Studies, Texas A and M University, College Station, Texas 77843-4242 (United States) and Physikalisches Institute, Universitaet Stuttgart, 70550 Stuttgart (Germany)

2007-10-15

30

Formation Dynamics of Ultra-Short Laser Induced Micro-Dots in the Bulk of Transparent Materials  

NASA Astrophysics Data System (ADS)

In this paper, we study the formation dynamics of ultra-short laser-induced micro dots under the surface of transparent materials. Laser-induced micro dots find their application in direct part marking, to address full life cycle traceability. We first demonstrate the possibility of direct laser part marking into the cladding of an optical fiber. Then, we monitor the laser affected zone with the help of a time-resolved phase contrast microscopy setup in a fused silica substrate. We show that the transient energy relaxation processes affect the host material over a region that exceeds the micro dot size by several micrometers.

Mermillod-Blondin, A.; Ashkenasi, D.; Lemke, A.; Schwagmeier, M.; Rosenfeld, A.

31

Dynamics of the laser-induced nanostructuring of thin metal layers: experiment and theory  

NASA Astrophysics Data System (ADS)

Nanostructures are of increasing importance in manifold application fields such as electronics, optics and beyond. However, the fast and cost-effective production of nanostructures is a big technological challenge for laser machining. One promising approach is laser irradiation of thin metal layers, which allows the fabrication of metal nanostructures induced by a melting and transformation process. The influence of laser parameters (laser fluence, laser pulse number) on the morphology of the nanopatterned film and the dynamics of the nanostructure formation during excimer laser irradiation of a 20 nm chromium film on fused silica were studied. The dynamics of nanopatterning, comprising hole and droplet formation, were investigated by time-dependent reflection and transmission measurements as well as time-dependent optical microscopy. The resulting patterns were investigated by optical and scanning electron microscopy (SEM). However, for an optimization of this process a better understanding of the underlying physical phenomena is necessary. Therefore, experimental data of laser-induced nanopatterning were compared with results of physical simulations that consider the heat equation (laser–solid interaction including melting and evaporation) and the Navier–Stokes equation (transformation processes of the molten phase). The simulations, making use of laser fluence-dependent effective material parameters (surface tension and viscosity), are in good agreement with the experimental results.

Lorenz, P.; Klöppel, M.; Smausz, T.; Csizmadia, T.; Ehrhardt, M.; Zimmer, K.; Hopp, B.

2015-02-01

32

Effect of the R dependence of laser-induced polarizability on molecular dynamic alignment in an intense femtosecond laser field  

NASA Astrophysics Data System (ADS)

In the rotation equation of the angle ? between the molecular axis and the laser polarization direction, the dependence of laser-induced polarizability on the molecular internuclear distance R is considered. The effect of the R dependence of laser-induced polarizability on molecular dynamic alignment in an intense femtosecond laser field is investigated with 20 and 100 fs laser pulses for N2 molecules and with 60 and 100 fs laser pulses for Br2 molecules at intensities of 5×1014 W cm-2 and 5×1015 W cm-2. This effect exists and only occurs during the dissociative process after the molecule is ionized. It enhances the degrees of molecular dynamic alignment and is more significant in reorienting the angular distributions of molecules towards the laser polarization direction in the conditions of high laser intensity and short pulse length. Compared with the N2 molecule, the effect of the R dependence of laser-induced polarizability on molecular dynamic alignment for Br2 is stronger. The reasons are presented and discussed.

Chen, Jianxin; Cui, Xiaomei; Huang, Bomin; Wu, Hongchun; Zhuo, Shuangmu

2006-12-01

33

Observation of Laser Induced Magnetization Dynamics in Co/Pd Multilayers with Coherent X-ray Scattering  

SciTech Connect

We report on time-resolved coherent x-ray scattering experiments of laser induced magnetization dynamics in Co/Pd multilayers with a high repetition rate optical pump x-ray probe setup. Starting from a multi-domain ground state, the magnetization is uniformly reduced after excitation by an intense 50 fs laser pulse. Using the normalized time correlation, we study the magnetization recovery on a picosecond timescale. The dynamic scattering intensity is separated into an elastic portion at length scales above 65 nm which retains memory of the initial domain magnetization, and a fluctuating portion at smaller length scales corresponding to domain boundary motion during recovery.

Wu, Benny

2012-04-05

34

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

NASA Astrophysics Data System (ADS)

Photoexcitation of 2-bromo-2-nitropropane (BNP) at 248 and 193 nm generates OH, Br, and NO2 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(X2?) 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 NO2 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(2P3/2) and Br*(2P1/2). 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.

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

2011-01-01

35

Dynamic strain measurements by fibre Bragg grating sensor  

Microsoft Academic Search

In this work, we describe a fibre Bragg grating (FBG) sensing system for static and dynamic strain measurements. Low cost and simple grating-based demodulation technique has been used to interrogate the strain induced Bragg wavelength shift. Experimental results showing the capability of the proposed system to perform static strain measurements with 1?? resolution and a linear response are presented. The

A. Cusano; A. Cutolo; J. Nasser; M. Giordano; A. Calabrò

2004-01-01

36

Dynamics of Pulsed Laser-Induced Metal Planarization and via Filling  

NASA Astrophysics Data System (ADS)

Multilevel thin-film interconnect, both on-chip and off-chip, is becoming an essential component in high -performance circuits and systems. Planarization and via filling techniques are necessary elements of a modern multilevel interconnect fabrication process. One such technique, pulsed laser induced metal planarization and via filling, is examined here. In this scheme, a pulsed laser is used to melt as-deposited metal structures so as to create a transient flow of molten metal which can, in the best case, completely planarize the metal and fill any vias which may be present. However, in some cases, the process is impractical because of void formation (in vias) or because it exhibits a process margin that is very narrow. Experimental and theoretical results that provide insight into the phenomena which currently limit this method's utility are presented here. Both a 600-ns pulse duration flashlamp-pumped dye laser and a 35-ns pulse duration excimer laser have been used to planarize features in as-deposited metal films. Thermal and hydrodynamic transients found in this process are modelled with a combination of analytical and numerical techniques. Small -amplitude bar patterns (square waves) on the surface of 2 ?m thick Au films have been fabricated and profiled before and after laser irradiation. These experiments reveal many of laser planarization's salient features, including a low-pass spatial filtering representation of the process, and excimer laser-induced evaporative-recoil -pressure effects. Metal (Au, Cu, and Al-1% Cu) coated vias and contact holes of varying size and aspect ratio have been fabricated and planarized with either of the aforementioned lasers. High aspect ratio (>1) vias and contact holes are found to be prone to formation of undesired voids. A simple mechanism, based on surface tension effects, explains why void formation is endemic when filling high aspect ratio vias and contact holes with this technique. It is shown (theoretically and experimentally) that the incident laser's pulse duration, or peak intensity, can be a key factor in determining process margins for laser planarization, and that, in many cases, evaporative recoil effects limit these margins for excimer laser planarization processes.

Marella, Paul Frank

37

Research towards development of a dynamic reflectometer for control of laser-induced retinal photocoagulation  

NASA Astrophysics Data System (ADS)

Laser-induced photocoagulation is used routinely to treat a variety of retinal disorders. In this procedure, absorption by the retina and choroid of focused laser light creates thermal lesions that provide the therapeutic effect. The treatment endpoint is determined by the ophthalmoscopical visibility of the coagulation resulting from the increased diffuse reflectivity of the fundus at the lesion site. To date, it is impossible, prior to treatment, to predict the effectiveness of a specific dosage of laser radiation -- the result can be assessed only after the exposure, and only subjectively. To avoid side effects like hemorrhage, macular pucker, and post-coagulative retinal detachments that can result from excessive local heating, a device for automatically controlling the laser exposure parameters is needed. Preliminary research aimed toward development of such a device has now been completed. The technique employs a simple electro-optical detector to monitor the changing reflectivity of the lesion during the laser exposure, and couples that information to a microcontroller which automatically adjusts the laser exposure parameters. The first results of a clinically realistic device are reported.

Frish, Michael B.; Pierce, Vicky G.; Ferguson, R. D.; Birngruber, Reginald

1992-08-01

38

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

39

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

40

Variable delay using stationary and localized Brillouin dynamic gratings  

NASA Astrophysics Data System (ADS)

Reflections from movable, dynamic acoustic gratings in polarization maintaining (PM) fibers are employed in the long variable delay of periodic, isolated pulses. The gratings are introduced by stimulated Brillouin scattering (SBS) interaction between two counter-propagating pump waves, which are spectrally detuned by the Brillouin frequency shift of the PM fiber and are both polarized along one of its principal axes. The gratings are interrogated by the reflections of read-out signals that are polarized along the orthogonal principal axis. High-rate phase modulation of both pump waves by a pseudo-random binary sequence introduces dynamic gratings that are both localized and stationary, at specific locations in which the modulated pumps are correlated. The separation between adjacent correlation peaks can be made arbitrarily long. Long variable delays are readily obtained by scanning the grating along the fiber, via changing either the length or the rate of the modulation sequence. At the same time, the short length of the gratings, on the order of a cm, accommodates the delay of broadband pulses. The technique is therefore free of the delay-times-bandwidth product limitation that undermines the performance of SBS-based 'slow light' delay: we report the delay 1-ns long pulses by as much as 770 ns. In addition, the combined reflections from two dynamic gratings with a variable separation are used to implement radio-frequency photonic filters of tunable free spectral range. At the current stage, the technique is restricted by noise from residual scattering that takes place outside of the correlation peaks. Hence, it is thus far limited to the processing of repetitive signals, for which the noise may be effectively averaged out.

Antman, Yair; Primerov, Nikolay; Sancho, Juan; Thévenaz, Luc; Zadok, Avi

2012-03-01

41

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

42

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

43

Influence of static pressure on dynamic characteristics of laser-induced cavitation and hard-tissue ablation under liquid environment  

NASA Astrophysics Data System (ADS)

Several studies have demonstrated that laser-induced hard tissue ablation effects can be enhanced by applying an additional water-layer on tissue surface. However, the related mechanism has not yet been presented clearly. In this paper, the influence of static pressure on dynamic characteristics of cavitation induced by pulse laser in liquid and its effect on bovine shank bone ablation were investigated. The laser source is fiber-guided free-running Ho:YAG laser with wavelength of 2080 nm, pulse duration of 350 ?s and energy of 1600 mJ. The tissue samples were immerged in pure water at different depths of 11, 16, 21, 26 and 31 mm. The working distance between the fiber tip and tissue surface was fixed at 1 mm for all studies. The dynamic interaction between laser, water and tissue were recorded by high-speed camera, and the morphological changes of bone tissue were assessed by stereomicroscope and OCT. The results showed that many times expansion and collapse of bubble were observed, more than four pulsation periods were accurately achieved with the most energy deposited in the first period and the bubble became more and more irregular in shape. The longitudinal length (7.49--6.74 mm) and transverse width (6.69--6.08 mm) of bubble were slowly decreased while volume (0.0586--0.0124 mm3) of ablation craters were drastically reduced, with static pressure increasing. The results also presented that the water-layer on hard-tissue surface can not only reduce thermal injury but also improve lubricity of craters, although the water-layer reduced ablation efficiency.

Chen, Chuanguo; Li, Xuwei; Zhang, Xianzeng; Zhan, Zhenlin; Xie, Shusen

2014-11-01

44

Generation of dynamic Brillouin grating in polarization maintaining fiber  

NASA Astrophysics Data System (ADS)

We report an experimental demonstration and characterization of dynamic Brillouin gratings (DBGs) in a 5m long polarization-maintaining fiber (PMF) using heterodyne detection. The dependence of DBG reflectivity on the Brillouin gain and on the pumps and the probe powers is studied and reported.

Sengupta, Dipankar; Santagiustina, Marco; Chiarello, Fabrizio; Palmieri, Luca

2014-09-01

45

Laser-induced femtosecond explosion dynamics of clusters and its effect on pulse self-focusing  

Microsoft Academic Search

We observe the femtosecond explosive dynamics of intense laser-heated clusters by measuring their transient polarizability. The evolution of the polarizability leads directly to pulse self-focusing . lntense laser interaction with atomic clusters is of great current interest. The generation of x-rays, fast electrons and ions, and fusion products are some of the applications, all of which are strongly affected by

K. Y. Kim; I. Alexeev; E. Parra; T. Antonsen; H. M. Milchberg

2003-01-01

46

Under-the-barrier dynamics in laser-induced relativistic tunneling  

E-print Network

The tunneling dynamics in relativistic strong-field ionization is investigated with the aim to develop an intuitive picture for the relativistic tunneling regime. We demonstrate that the tunneling picture applies also in the relativistic regime by introducing position dependent energy levels. The quantum dynamics in the classically forbidden region features two time scales, the typical time that characterizes the probability density's decay of the ionizing electron under the barrier (Keldysh time) and the time interval which the electron spends inside the barrier (Eisenbud-Wigner-Smith tunneling time). In the relativistic regime, an electron momentum shift as well as a spatial shift along the laser propagation direction arise during the under-the-barrier motion which are caused by the laser magnetic field induced Lorentz force. The momentum shift is proportional to the Keldysh time, while the wave-packet's spatial drift is proportional to the Eisenbud-Wigner-Smith time. The signature of the momentum shift is shown to be present in the ionization spectrum at the detector and, therefore, observable experimentally. In contrast, the signature of the Eisenbud-Wigner-Smith time delay disappears at far distances for pure quasistatic tunneling dynamics.

Michael Klaiber; Enderalp Yakaboylu; Heiko Bauke; Karen Z. Hatsagortsyan; Christoph H. Keitel

2012-05-09

47

Under-the-barrier dynamics in laser-induced relativistic tunneling.  

PubMed

The tunneling dynamics in relativistic strong-field ionization is investigated with the aim to develop an intuitive picture for the relativistic tunneling regime. We demonstrate that the tunneling picture applies also in the relativistic regime by introducing position dependent energy levels. The quantum dynamics in the classically forbidden region features two time scales, the typical time that characterizes the probability density's decay of the ionizing electron under the barrier (Keldysh time) and the time interval which the electron spends inside the barrier (Eisenbud-Wigner-Smith tunneling time). In the relativistic regime, an electron momentum shift as well as a spatial shift along the laser propagation direction arise during the under-the-barrier motion which are caused by the laser magnetic field induced Lorentz force. The momentum shift is proportional to the Keldysh time, while the wave-packet's spatial drift is proportional to the Eisenbud-Wigner-Smith time. The signature of the momentum shift is shown to be present in the ionization spectrum at the detector and, therefore, observable experimentally. In contrast, the signature of the Eisenbud-Wigner-Smith time delay disappears at far distances for pure quasistatic tunneling dynamics. PMID:25167261

Klaiber, Michael; Yakaboylu, Enderalp; Bauke, Heiko; Hatsagortsyan, Karen Z; Keitel, Christoph H

2013-04-12

48

Molecular dynamics simulations of laser-induced incandescence of soot using an extended ReaxFF reactive force field.  

PubMed

Laser-induced incandescence (LII) of soot has developed into a popular method for making in situ measurements of soot volume fraction and primary particle sizes. However, there is still a lack of understanding regarding the generation and interpretation of the cooling signals. To model heat transfer from the heated soot particles to the surrounding gas, knowledge of the collision-based cooling as well as reactive events, including oxidation (exothermic) and evaporation (endothermic) is essential. We have simulated LII of soot using the ReaxFF reactive force field for hydrocarbon combustion. Soot was modeled as a stack of four graphene sheets linked together using sp(3) hybridized carbon atoms. To calculate the thermal accommodation coefficient of various gases with soot, graphene sheets of diameter 40 Å were used to create a soot particle containing 2691 atoms, and these simulations were carried out using the ReaxFF version incorporated into the Amsterdam Density Functional program. The reactive force field enables us to simulate the effects of conduction, evaporation, and oxidation of the soot particle on the cooling signal. Simulations were carried out for both reactive and nonreactive gas species at various pressures, and the subsequent cooling signals of soot were compared and analyzed. To correctly model N(2)-soot interactions, optimization of N-N and N-C-H force field parameters against DFT and experimental values was performed and is described in this paper. Subsequently, simulations were performed in order to find the thermal accommodation coefficients of soot with various monatomic and polyatomic gas molecules like He, Ne, Ar, N(2), CO(2), and CH(4). For all these species we find good agreement between our ReaxFF results and previously published accommodation coefficients. We thus believe that Molecular Dynamics using the ReaxFF reactive force field is a promising approach to simulate the physical and chemical aspects of soot LII. PMID:21067165

Kamat, Amar M; van Duin, Adri C T; Yakovlev, Alexei

2010-12-01

49

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

50

All-optical signal processing using dynamic Brillouin gratings  

PubMed Central

The manipulation of dynamic Brillouin gratings in optical fibers is demonstrated to be an extremely flexible technique to achieve, with a single experimental setup, several all-optical signal processing functions. In particular, all-optical time differentiation, time integration and true time reversal are theoretically predicted, and then numerically and experimentally demonstrated. The technique can be exploited to process both photonic and ultra-wide band microwave signals, so enabling many applications in photonics and in radio science. PMID:23549159

Santagiustina, Marco; Chin, Sanghoon; Primerov, Nicolay; Ursini, Leonora; Thévenaz, Luc

2013-01-01

51

Terahertz emission spectroscopy of laser-induced spin dynamics in TmFeO3 and ErFeO3 orthoferrites  

NASA Astrophysics Data System (ADS)

Using the examples of laser-induced spin-reorientation phase transitions in TmFeO3 and ErFeO3 orthoferrites, we demonstrate that terahertz emission spectroscopy can obtain novel information about ultrafast laser-induced spin dynamics, which is not accessible by more common all-optical methods. The power of the method is evidenced by the fact that, in addition to the expected quasi-ferromagnetic and quasi-antiferromagnetic modes of the iron sublattices, terahertz emission spectroscopy enables detection of a resonance optically excited at an unexpected frequency of ˜0.3-0.35 THz. By recording how the amplitude and phase of the excited oscillations depend on temperature and applied magnetic field, we show that the unexpected mode has all the features of a spin resonance of the Fe3 + ions. We suggest that it can be assigned to transitions between the multiplet sublevels of the 6A1 ground state of the Fe+3 ions occupying rare-earth positions.

Mikhaylovskiy, R. V.; Hendry, E.; Kruglyak, V. V.; Pisarev, R. V.; Rasing, Th.; Kimel, A. V.

2014-11-01

52

Study of collisional deactivation of O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings  

SciTech Connect

Collisional deactivation of O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H{sub 2}/O{sub 2} mixtures is experimentally studied. The radiation intensity and hence the molecule excitation efficiency have a spatially periodic modulation that leads to the formation of laser-induced gratings (LIGs) of the refractive index. The study of LIG temporal evolution allows collisional relaxation rates of molecular excited states and gas temperature to be determined. In this work, the b{sup 1}{Sigma}{sub g}{sup +} state of O{sub 2} molecules deactivation rates are measured in a 4.3 vol % H{sub 2} mixture at the number density of 2 amg in the temperature range 291-850 K. The physical deactivation is shown to dominate in the collisions of H{sub 2} with O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) and O{sub 2}(a{sup 1}{Delta}{sub g}) up to temperatures of 780-790 K at time delays up to 10 {mu}s after the excitation pulse. The parameters of the obtained temperature dependence of the (b{sup 1}{Sigma}{sub g}{sup +} state deactivation rate agree well with the data of independent measurements performed earlier at lower temperatures (200-400 K). Tunable diode laser absorption spectroscopy is used to measure the temperature dependence of the number density of the H{sub 2}O molecules which appear as the mixture, as the result of the dark gross reaction with O{sub 2} molecules in the ground state, O{sub 2} + 2H{sub 2} {yields} 2H{sub 2}O. The measurements show that this reaction results in complete transformation of H{sub 2} into H{sub 2}O at temperatures of 790-810 K.

Kozlov, D. N., E-mail: dnk@kapella.gpi.ru; Kobtsev, V. D.; Stel'makh, O. M.; Smirnov, V. V. [Russian Academy of Sciences, A.M. Prokhorov General Physics Institute (Russian Federation)] [Russian Academy of Sciences, A.M. Prokhorov General Physics Institute (Russian Federation)

2013-07-15

53

Gelator-doped liquid-crystal phase grating with multistable and dynamic modes  

SciTech Connect

We demonstrate a gelator-doped nematic liquid-crystal (LC) phase grating, which can be operated in both the multistable mode and the dynamic mode. Thermoreversible association and dissociation of the gelator molecules can vary and fix the multistable diffraction efficiencies of the gratings. A voltage (V) can also be applied to modulate dynamically the diffraction efficiencies of the grating, which behaves as a conventional LC grating. Experimental results show that the variations of the diffraction efficiencies in the multistable and dynamic modes are similar. The maximum diffraction efficiency is approximately 30% at V?=?2?V.

Lin, Hui-Chi, E-mail: huichilin@nfu.edu.tw; Yang, Meng-Ru; Tsai, Sheng-Feng; Yan, Shih-Chiang [Department of Electro-Optical Engineering, National Formosa University, Yunlin 632, Taiwan (China)] [Department of Electro-Optical Engineering, National Formosa University, Yunlin 632, Taiwan (China)

2014-01-06

54

Nanometer Photothermal Heating and Cooling Dynamics of Azo Polymer Film Elucidated by Analyzing Nanosecond Laser-Induced Expansion/Contraction Behavior  

NASA Astrophysics Data System (ADS)

The nanosecond transient expansion and successive contraction dynamics of an azobenzene-substituted urethane-urea copolymer film were studied by nanosecond time-resolved interferometry. In addition, the photoisomerization dynamics of azo dyes during morphological change was investigated by transient absorption measurement. A transiently generated cis isomer absorbed a few photons during laser irradiation and its energy was effectively converted to heat. When the pulse width of the irradiated laser was 8 or 14 ns full-width at half maximum (fwhm), the expansion of the polymer film started with 3-6 ns delay from the temperature elevation, while the film contracted exponentially accompanying a different absorbance change of the transient species. The expansion dynamics was well explained not in terms of volume change due to isomerization dynamics but in terms of thermal expansion involving glass-rubber transition. The film-thickness-dependent contraction dynamics could be mostly interpreted in view of the heat flow toward the quartz substrate, heat dissipation via the film itself, and phase transition of the polymer film from the rubbery to glassy states. The laser-induced transient morphological change of the urethane-urea copolymer film observed below the threshold could be well explained in terms of nanometer heating and cooling dynamics.

Tada, Takuji; Asahi, Tsuyoshi; Tsuchimori, Masaaki; Watanabe, Osamu; Masuhara, Hiroshi

2004-08-01

55

Laser-induced magnetization curve  

NASA Astrophysics Data System (ADS)

We propose an all optical ultrafast method to highly magnetize general quantum magnets using a circularly polarized terahertz laser. The key idea is to utilize a circularly polarized laser and its chirping. Through this method, one can obtain magnetization curves of a broad class of quantum magnets as a function of time even without any static magnetic field. We numerically demonstrate the laser-induced magnetization process in realistic quantum spin models and find a condition for the realization. The onset of magnetization can be described by a many-body version of Landau-Zener mechanism. In a particular model, we show that a plateau state with topological properties can be realized dynamically.

Takayoshi, Shintaro; Sato, Masahiro; Oka, Takashi

2014-12-01

56

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

57

Laser-induced electron dynamics including photoionization: A heuristic model within time-dependent configuration interaction theory.  

PubMed

We report simulations of laser-pulse driven many-electron dynamics by means of a simple, heuristic extension of the time-dependent configuration interaction singles (TD-CIS) approach. The extension allows for the treatment of ionizing states as nonstationary states with a finite, energy-dependent lifetime to account for above-threshold ionization losses in laser-driven many-electron dynamics. The extended TD-CIS method is applied to the following specific examples: (i) state-to-state transitions in the LiCN molecule which correspond to intramolecular charge transfer, (ii) creation of electronic wave packets in LiCN including wave packet analysis by pump-probe spectroscopy, and, finally, (iii) the effect of ionization on the dynamic polarizability of H(2) when calculated nonperturbatively by TD-CIS. PMID:19778110

Klinkusch, Stefan; Saalfrank, Peter; Klamroth, Tillmann

2009-09-21

58

Laser-induced ultrafast spin dynamics in di-, tri- and tetranuclear nickel clusters, and the M process  

NASA Astrophysics Data System (ADS)

In this manuscript we present an ab initio picture of ultrafast magneto-optical dynamics in clusters containing 2, 3, and 4 Ni atoms. The presence of the magnetic centers in the clusters renders our systems of choice highly interesting for studying ultrafast spin dynamics. Here we systematically study functional cooperativity by increasing both the number of active centers and the spin multiplicities included in our Hilbert space (singlets ? triplets ? quintets), and deriving several ultrafast, laser-driven, spin-manipulation scenarios. Our results indicate various cooperative effects like spin flip by the M process, and simultaneous spin flip and spin transfer, as well as reversible and irreversible demagnetization scenarios. As it turns out the functional cooperativity of the clusters strongly benefits from the delicate interplay of the spin multiplicity and the number of active centers.

Chaudhuri, D.; Xiang, H. P.; Lefkidis, G.; Hübner, W.

2014-12-01

59

Dynamic monitoring of grating angle at the National Synchrotron Light Source  

NASA Astrophysics Data System (ADS)

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, Shinan; Arena, Darío; Dvorak, Joseph; Qian, Kun

2009-11-01

60

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

61

Investigation of grating dynamics using a phase conjugate mirror  

NASA Astrophysics Data System (ADS)

Presented are results of fast (ns) grating formation and decay in the semiconductor gallium phosphide and an acridine dye doped glass saturable absorber measured by a new pump-probe technique. In both cases a moveable BaTiO 3 phase conjugate mirror was used to effect a delayed probe pulse with a reflectivity of ˜50% over a wide range of mode-locked and Q-switched mode-locked repetition rates at 532 nm. The advantages of our pump-probe scheme are considered which has enabled the first measurements of singlet and excited triplet state grating formation in acridine doped glass to be performed and also to distinguish between competing processes of free-carrier and thermal grating formation in GaP.

Shimura, T.; Boothroyd, S. A.; Chrostowski, J.; Myslinski, P.

1993-08-01

62

Colorizing pure copper surface by ultrafast laser-induced near-subwavelength ripples.  

PubMed

We demonstrate that the colorizing effect of angle dependence can be efficiently and conveniently achieved on the rippled surface of pure copper processed by the femtosecond laser with an out-of-focus method, which greatly improves the machining speed. Such a laser-induced colorization can occur in a wide range of laser fluence, which determines the coverage and morphological characteristics of laser-induced ripples and thus can finely tune the colorizing effect. By inspecting the colors and corresponding spectra of treated areas at different angles, the relationship between the diffracted light central wavelength and the laser-induced near-subwavelength grating is analyzed quantitatively based on the fundamental grating equation with the experimental grating parameters. The spectrum analysis indicates that for the laser fluence increasing in a suitable range, the more clarity and regularity of formed ripples should bring out a more prominent grating effect, which becomes further matching of the grating equation in a larger inspecting angle for the elimination of the influence of the diffused reflection light. In short, the study confirms that the colorizing phenomenon mainly ascribes to the grating diffraction effect of the laser-induced periodic surface ripples, which would help to enable the flexible control of the colorizing effect induced by laser processing on pure copper. PMID:25090539

Ou, Zhigui; Huang, Min; Zhao, Fuli

2014-07-14

63

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

SciTech Connect

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., E-mail: jiaxin@sdju.edu.cn [State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062 (China); Department of Mathematics and Physics, Shanghai Dianji University, Shanghai 201306 (China); Jia, T. Q., E-mail: tqjia@phy.ecnu.edu.cn; Peng, N. N.; Feng, D. H.; Zhang, S. A.; Sun, Z. R. [State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062 (China)

2014-04-14

64

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

65

Structural and Magnetic Dynamics of a Laser Induced Phase Transition in FeRh S. O. Mariager,1,* F. Pressacco,2  

E-print Network

-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic-optical Kerr effect (TR- MOKE) [12,13]. While the reflectivity measures a combi- nation of electronic laser pulses. The first order phase transition from the low temperature AFM phase is accompanied by a $0

Wang, Deli

66

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

67

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

68

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

69

Dynamic mechanistic model of superheater deposit growth and shedding in a biomass fired grate boiler  

Microsoft Academic Search

A dynamic mathematical model of ash deposit growth and shedding on a horizontal cooled probe in a straw fired grate boiler has been developed and validated. The model includes submodels of deposition (impaction, thermophoresis, Brownian and eddy diffusion, and condensation) and shedding by deposit surface melting. Three new submodels describing deposit formation on the downstream side of the probe, ash

Haosheng Zhou; Peter Arendt Jensen; Flemming Jappe Frandsen

2007-01-01

70

Quenched by ice: Transient grating measurements of vibronic dynamics in bromine-doped ice  

E-print Network

Quenched by ice: Transient grating measurements of vibronic dynamics in bromine-doped ice I. U April 2006; published online 25 May 2006 In both water and in ice, the absorption spectra of bromine of clathrate hydrates,1,2 bromine hydrate being one of the earliest discovered.3 The concept is to use

Apkarian, V. Ara

71

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

72

Dynamics of the formation of laser-induced periodic surface structures on dielectrics and semiconductors upon femtosecond laser pulse irradiation sequences  

NASA Astrophysics Data System (ADS)

The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica and silicon with multiple ( N DPS) irradiation sequences consisting of linearly polarized femtosecond laser pulse pairs (pulse duration ˜150 fs, central wavelength ˜800 nm) is studied experimentally. Nearly equal-energy double-pulse sequences are generated allowing the temporal pulse delay ? t between the cross-polarized individual fs-laser pulses to be varied from -40 ps to +40 ps with a resolution of ˜0.2 ps. The surface morphologies of the irradiated surface areas are characterized by means of scanning electron and scanning force microscopy. Particularly for dielectrics in the sub-ps delay range striking differences in the orientation and spatial characteristics of the LIPSS can be observed. For fused silica, a significant decrease of the LIPSS spatial periods from ˜790 nm towards ˜550 nm is demonstrated for delay changes of less than ˜2 ps. In contrast, for silicon under similar irradiation conditions, the LIPSS periods remain constant (˜760 nm) for delays up to 40 ps. The results prove the impact of laser-induced electrons in the conduction band of the solid and associated transient changes of the optical properties on fs-LIPSS formation.

Höhm, S.; Rohloff, M.; Rosenfeld, A.; Krüger, J.; Bonse, J.

2013-03-01

73

Single grating x-ray imaging for dynamic biological systems  

NASA Astrophysics Data System (ADS)

Biomedical studies are already benefiting from the excellent contrast offered by phase contrast x-ray imaging, but live imaging work presents several challenges. Living samples make it particularly difficult to achieve high resolution, sensitive phase contrast images, as exposures must be short and cannot be repeated. We therefore present a single-exposure, high-flux method of differential phase contrast imaging [1, 2, 3] in the context of imaging live airways for Cystic Fibrosis (CF) treatment assessment [4]. The CF study seeks to non-invasively observe the liquid lining the airways, which should increase in depth in response to effective treatments. Both high spatial resolution and sensitivity are required in order to track micron size changes in a liquid that is not easily differentiated from the tissue on which it lies. Our imaging method achieves these goals by using a single attenuation grating or grid as a reference pattern, and analyzing how the sample deforms the pattern to quantitatively retrieve the phase depth of the sample. The deformations are mapped at each pixel in the image using local cross-correlations comparing each 'sample and pattern' image with a reference 'pattern only' image taken before the sample is introduced. This produces a differential phase image, which may be integrated to give the sample phase depth.

Morgan, Kaye S.; Paganin, David M.; Parsons, David W.; Donnelley, Martin; Yagi, Naoto; Uesugi, Kentaro; Suzuki, Yoshio; Takeuchi, Akihisa; Siu, Karen K. W.

2012-07-01

74

Aspects of Laser Induced Fluorescence Employing Pulsed and Modulated Excitation  

Microsoft Academic Search

This work reports on various aspects of employing strong, pulsed or modulated excitation in laser induced fluorescence (LIF) experiments. Part I is motivated by two-photon LIF measurements in nitric oxide, used for the determination of temperatures and concentrations in cold flows. It is found that dynamical Stark effects modify the lineshapes of individual rotational transitions significantly, thereby invalidating conventional methods

Wilhelmus M. J. Ruyten

1989-01-01

75

A novel distributed strain sensor based on dynamic grating in polarization-maintaining erbium-doped fiber  

Microsoft Academic Search

We report the experimental demonstration of a novel distributed fiber-optic strain sensor by localizing a dynamic grating in polarization maintaining erbium-doped fiber (PM-EDF) using the technique of synthesis of optical coherence function (SOCF).

Xinyu Fan; Zuyuan He; K. Hotate

2006-01-01

76

Localized and stationary dynamic gratings via stimulated Brillouin scattering with phase modulated pumps.  

PubMed

A novel technique for the localization of stimulated Brillouin scattering (SBS) interaction is proposed, analyzed and demonstrated experimentally. The method relies on the phase modulation of two counter-propagating optical waves by a common pseudo-random bit sequence (PRBS), these waves being spectrally detuned by the Brillouin frequency shift. The PRBS symbol duration is much shorter than the acoustic lifetime. The interference between the two modulated waves gives rise to an acoustic grating that is confined to narrow correlation peaks, as short as 1.7 cm. The separation between neighboring peaks, which is governed by the PRBS length, can be made arbitrarily long. The method is demonstrated in the generation and applications of dynamic gratings in polarization maintaining (PM) fibers. Localized and stationary acoustic gratings are induced by two phase modulated pumps that are polarized along one principal axis of the PM fiber, and interrogated by a third, readout wave which is polarized along the orthogonal axis. Using the proposed technique, we demonstrate the variable delay of 1 ns-long readout pulses by as much as 770 ns. Noise due to reflections from residual off-peak gratings and its implications on the potential variable delay of optical communication data are discussed. The method is equally applicable to the modulation of pump and probe waves in SBS over standard fibers. PMID:22453458

Antman, Y; Primerov, N; Sancho, J; Thevenaz, L; Zadok, A

2012-03-26

77

Laser Induced Fluorescence Spectroscopy of Cobalt Monoboride  

NASA Astrophysics Data System (ADS)

Laser induced fluorescence spectrum of cobalt monoboride (CoB) in the visible region between 465 and 560 nm has been observed. CoB molecule was produced by the reaction of laser ablated cobalt atom and diborane (B_2H_6) seeded in argon. Over twenty five vibronic bands have been recorded, and both Co10B and Co11B isotopic species have been observed and analyzed. Preliminary analysis of the rotational lines showed that the observed vibronic bands belong to two categories namely: the ?' = 2 - ?'' = 2 and the ?' = 3 - ?'' = 3 transitions, which indicated the ground state of CoB is consistent with an assignment of a ^3?_i state predicted from ab initio calculations. Unresolved hyperfine structure arising from the Co nucleus (I = 7/2) causes a broadening of spectral lines. This work represents the first experimental investigation of the spectrum of the CoB molecule. Financial support from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKU 701008P) is gratefully acknowledged.

Pang, H. F.; Ng, Y. W.; Cheung, A. S.-C.

2011-06-01

78

The photodissociation and reaction dynamics of vibrationally excited molecules  

SciTech Connect

This research determines the nature of highly vibrationally excited molecules, their unimolecular reactions, and their photodissociation dynamics. The goal is to characterize vibrationally excited molecules and to exploit that understanding to discover and control their chemical pathways. Most recently the author has used a combination of vibrational overtone excitation and laser induced fluorescence both to characterize vibrationally excited molecules and to study their photodissociation dynamics. The author has also begun laser induced grating spectroscopy experiments designed to obtain the electronic absorption spectra of highly vibrationally excited molecules.

Crim, F.F. [Univ. of Wisconsin, Madison (United States)

1993-12-01

79

The photodissociation and reaction dynamics of vibrationally excited molecules  

SciTech Connect

We have used combined vibrational overtone excitation and laser induced fluorescence detection to study dissociation dynamics of hydroxylamine (NH[sub 2]OH), have performed our first laser induced grating experiments on water, and have begun assembling a new apparatus for preparing vibrationally excited molecules with simulated Raman excitation. We study role of vibrational excitation in photodissociation dynamics by using a vibrational state preparation technique, such as vibrational overtone excitation or stimulated Raman excitation, to create molecules with particular nuclear motions and then to excite that molecule to a dissociative electronic state.

Not Available

1993-01-01

80

Dynamic response of QWS-DFB lasers with convex tapered grating structure and non-zero facet reflection  

NASA Astrophysics Data System (ADS)

Using finite difference time domain (FDTD) method, we analyze static and dynamic response of non-uniform grating quarter-wavelength shift distributed feedback QWS-DFB laser with non-zero facet reflection coefficients, both for large signal transient and small signal modulation. By introducing a convex tapered grating structure for QWS-DFB laser (XTG-DFB), it is shown that single mode stability of laser enhances and laser is less sensitive to random phase of reflection coefficients. We also show that XTG-DFB laser has better small signal response in comparison with uniform grating QWS-DFB laser.

Bazhdanzadeh, N.; Ahmadi, V.; Ghafoorifard, H.; Shahshahani, F.

2008-02-01

81

Novel Distributed Fiber-Optic Strain Sensor by Localizing Dynamic Grating in Polarization-Maintaining Erbium-Doped Fiber: Proposal and Theoretical Analysis  

Microsoft Academic Search

A novel scheme of distributed fiber-optic strain sensor by localizing a dynamic grating in a polarization-maintaining erbium-doped fiber is proposed. The dynamic grating, which is introduced by launching two counterpropagating coherent light beams into a pumped erbium-doped fiber per gain saturation, is examined. A theoretical model of the dynamic grating is given and used to perform simulations of the reflectivity

Xinyu Fan; Zuyuan He; Kazuo Hotate

2005-01-01

82

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

83

Laser induced melting and crystallization of boron doped amorphous silicon  

SciTech Connect

Transient reflectivity experiments have been performed to measure the dynamics of laser-induced melting of amorphous silicon (a-Si) and the crystallization to {micro}c-Si of films with different thicknesses on Corning 7059 glass. The laser-induced melting takes place with a velocity of 13 to 24 m/s, while the solidification is about a factor 10 slower. The crystallization starts at the Si/glass interface and at the surface. In the center of the films Si remains liquid for an extended period of time. The crystallization dynamics point towards an heterogeneous morphology of laser-crystallized Si, where the surface and the interface layers are composed of small grains and the bulk of larger grains.

Nebel, C.E.; Schoeniger, S.; Dahlheimer, B.; Stutzmann, M.

1997-07-01

84

The photodissociation and reaction dynamics of vibrationally excited molecules. Technical progress report, 1992--1993  

SciTech Connect

We have used combined vibrational overtone excitation and laser induced fluorescence detection to study dissociation dynamics of hydroxylamine (NH{sub 2}OH), have performed our first laser induced grating experiments on water, and have begun assembling a new apparatus for preparing vibrationally excited molecules with simulated Raman excitation. We study role of vibrational excitation in photodissociation dynamics by using a vibrational state preparation technique, such as vibrational overtone excitation or stimulated Raman excitation, to create molecules with particular nuclear motions and then to excite that molecule to a dissociative electronic state.

Not Available

1993-04-01

85

Laser-induced tether & spouts  

NASA Astrophysics Data System (ADS)

Since the seminal work of Ashkin and Dziedzic on the deformation of transparent free-surfaces induced by laser waves, the optical radiation pressure has been recognized as very appealing to locally manipulate liquid interfaces. While the first developments essentially exploited the interface bending for optical applications in adaptive lensing, radiation pressure effects have recently received renewed interest in connection with nano/bio-technologies, as a non-intrusive tool to probe microscopic surface properties of soft materials including cell stretching, or membrane and interface visco-elasticity. However, as the optical bending of a fluid interface is generally weak, these experiments were essentially limited to the linear regime in deformation. Non-linear behaviors can nevertheless be investigated using very soft transparent liquid interfaces to enhance light effects. At large optical excitation, either a large stable tether is formed, or else a break-up of the interface occurs, depending on the direction of the beam propagation. Physically, the reason for this asymmetry can be traced to whether total reflection of light at deformed interface occurs or not. Laser-induced interface instability leads to the formation of a stationary beam-centered liquid micro-jet emitting droplets, which anticipates the bases for new applications in micro-fluidics and liquid micro-spraying. On the other hand, the method can be extended to form microscopic liquid bridges of very large aspect ratio, because optical forces are able to overcome the fundamental Rayleigh-Plateau limitation. As laser-induced micro-jets, laser-sustained liquid columns are tunable in aspect ratio and adjustable in direction. Consequently, the applications range of "opto-hydrodynamic" interface instability is wide, going from micro-optics (i.e. liquid columns also behave as soft optical fibers) to micro-fluidics, as fluid transfer can be optically monitored and directed in three dimensions.

Delville, Jean-Pierre

2004-03-01

86

Dynamic trapping of terahertz waves by silicon-filled metallic grating structure  

NASA Astrophysics Data System (ADS)

We investigate the feasibility of dynamic trapping of terahertz waves using a silicon-filled metallic grating structure. Using the dispersion relation analysis and the two-dimensional finite element method simulations, we reveal that, if a graded refractive index distribution in the grooves is optical induced, the device has the ability to dynamic trap terahertz waves of different frequencies at different positions (so-called trapping rainbow). Moreover, we demonstrate that the trapped position of a certain frequency of the terahertz waves can be moved continuously along the grooves in subwavelength scale by ingenious control of the distributions of the refractive indices of silicon filled in the grooves. Our design has the potential for the construction of active plasmonic terahertz devices, such as optical controlled terahertz filter, router and demultiplexer in a broadband terahertz communication system.

Yuan, Yinghao; Liu, Jinsong; He, Jian; Yao, Jianquan

2014-12-01

87

Interaction between jets during laser-induced forward transfer  

SciTech Connect

Simultaneous two-beam laser-induced forward transfer (LIFT) was carried out for various inter-beam separations, analyzing both the resulting printing outcomes and the corresponding liquid transfer dynamics. In a first experiment, droplets of an aqueous solution were printed onto a substrate at different inter-beam distances, which proved that a significant departure from the single-beam LIFT dynamics takes places at specific separations. In the second experiment, time-resolved imaging analysis revealed the existence of significant jet-jet interactions at those separations; such interactions proceed through a dynamics that results in remarkable jet deflection for which a possible onset mechanism is proposed.

Patrascioiu, A.; Florian, C.; Fernández-Pradas, J. M.; Morenza, J. L.; Serra, P., E-mail: pserra@ub.edu [Departament de Física Aplicada i Òptica, Universitat de Barcelona, Martí i Franquès 1, E-08028 Barcelona (Spain); Hennig, G. [DI Projekt AG, Flugplatz, CH-3368 Bleienbach (Switzerland); Delaporte, P. [Aix Marseille University, CNRS, LP3 UMR 7341, 163 Avenue de Luminy, 13288 Marseille (France)

2014-07-07

88

Interaction between jets during laser-induced forward transfer  

NASA Astrophysics Data System (ADS)

Simultaneous two-beam laser-induced forward transfer (LIFT) was carried out for various inter-beam separations, analyzing both the resulting printing outcomes and the corresponding liquid transfer dynamics. In a first experiment, droplets of an aqueous solution were printed onto a substrate at different inter-beam distances, which proved that a significant departure from the single-beam LIFT dynamics takes places at specific separations. In the second experiment, time-resolved imaging analysis revealed the existence of significant jet-jet interactions at those separations; such interactions proceed through a dynamics that results in remarkable jet deflection for which a possible onset mechanism is proposed.

Patrascioiu, A.; Florian, C.; Fernández-Pradas, J. M.; Morenza, J. L.; Hennig, G.; Delaporte, P.; Serra, P.

2014-07-01

89

Mask pattern transferred transient grating technique for molecular-dynamics study in solutions  

E-print Network

transferred transient grating (MPT-TG) technique by using metal grating films. Transient thermal grating is generated by an ultraviolet light pattern transfer to nitrobenzene in 2-propanol solution by an optical interference pattern generated by two crossing pump beams. As parameters, sev- eral properties

Okamoto, Koichi

90

Laser-induced plasma temperature  

NASA Astrophysics Data System (ADS)

It is of great importance to explore the evolution of laser-induced plasma (LIP) properties, especially plasma temperature, with regard to variations of experiment conditions in both theoretical study and routine applications. By investigating the influence of various factors on plasma temperature, one can gain knowledge about the processes in plasma and adjust experimental conditions to obtain optimum analytical performance. Herein the fundamental theories and calculation methods of LIP temperature via spectroscopic approaches are briefly reviewed. Its temporal and spatial evolutions together with several influencing factors are discussed, such as laser parameters, ambient surrounding, and physical & chemical properties of the sample. The results summarized exhibit the general trend that LIP temperature increases with increasing laser wavelength, pulse width, laser energy, background gas pressure, and sample hardness. On the other hand, it decreases with time elapsing and distance from sample surface. Moreover, plasma temperature generated in argon surrounding is higher than that in other gas species, and the rank of temperature values generated from different samples exhibits a general tendency of Cu > Fe > Ni ? Al ? glass ? rock. Additionally, LIP temperature tends to increase as lens focal point approaches sample surface, and the plasma confinement effect in sample cavity is significant in altering plasma temperature. Various explanations are given to interpret these temperature behaviors.

Zhang, Shudi; Wang, Xiaohua; He, Miaohong; Jiang, Yunbin; Zhang, Bochao; Hang, Wei; Huang, Benli

2014-07-01

91

Record of thin dynamic holographic grating with asymmetrical fringe profile in optical feedback loop with TV-closure  

NASA Astrophysics Data System (ADS)

In this paper we present results of theoretical and experimental research of dynamic holographic system based on optically-addressed liquid crystal light modulator inside optical feedback loop, which provides asymmetrization of grating's profile. We use computer-based signal loop instead of pure optical link. This approach gives us solution for hysteresis problems and significantly reduces optical scheme complexity.

Venediktov, V. Yu.; Freygang, N. N.; Laskin, V. A.

2009-05-01

92

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.

2006-02-01

93

Molecular dynamics in azobenzene liquid crystal polymer films studied by transient grating technique  

NASA Astrophysics Data System (ADS)

We studied the effect of the ratio between the monomer and cross-linker molecules in the azobenene included liquid crystal polymer films by using the heterodyne transient grating (HD-TG) technique, which is one of the time-resolved measurement techniques. Depending on the ratio, the magnitude of the refractive index change, its anisotropy, and the lifetime of the cis isomer of azobenzene, generated by a UV pulse irradiation. By increasing the cross-linker ratio, the refractive index change and its anisotropy was reduced, indicating less ability for the motion, while slower lifetime was observed by increasing the monomer ratio, indicating that the film is difficult to return the original shape by a visiblelight irradiation. The obtained dynamics was consistent with the functionality of the films.

Katayama, Kenji; Fujii, Tomomi; Kuwahara, Shota; Takado, Kiyohide; Ikeda, Tomiki

2014-10-01

94

Carrier Dynamics in InGaN/GaN SQW Structure Probed by the Transient Grating Method  

E-print Network

Carrier Dynamics in InGaN/GaN SQW Structure Probed by the Transient Grating Method; 78.55.Cr; 78.67.De; S7.14 Carrier dynamics in GaN and InGaN/GaN SQW structures were observed by using inhomogeneity of In composition. Recently, InGaN/GaN-based light emitting diodes (LEDs) have been commercialized

Okamoto, Koichi

95

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

SciTech Connect

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

Pennington, D.M.; Harris, C.B. [California Univ., Berkeley, CA (United States). Dept. of Chemistry

1993-02-01

96

Long-lived laser-induced microwave plasma guides in the atmosphere: Self-consistent plasma-dynamic analysis and numerical simulations  

SciTech Connect

A detailed model of plasma dynamics, which self-consistently integrates plasma-kinetic, Navier-Stokes, electron heat conduction, and electron-vibration energy transfer equations, is used to quantify the limitations on the lifetime of microwave plasma waveguides induced in the atmosphere through filamentation with high-intensity ultrashort laser pulses further sustained by long laser pulses. We demonstrate that a near-infrared or midinfrared laser pulse can tailor plasma decay in the wake of a filament, efficiently suppressing, through electron temperature increase, the attachment of electrons to neutral species and dissociative recombination, thus substantially increasing the plasma-guide lifetime and facilitating long-distance transmission of microwaves.

Shneider, M. N.; Miles, R. B. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544-5263 (United States); Zheltikov, A. M. [Department of Physics, International Laser Center, M. V. Lomonosov Moscow State University, Moscow 119992 (Russian Federation)

2010-08-15

97

Laser-induced caesium-137 decay  

NASA Astrophysics Data System (ADS)

Experimental data are presented on the laser-induced beta decay of caesium-137. We demonstrate that the exposure of a gold target to a copper vapour laser beam (wavelengths of 510.6 and 578.2 nm, pulse duration of 15 ns) for 2 h in an aqueous solution of a caesium-137 salt reduces the caesium-137 activity by 70%, as assessed from the gamma activity of the daughter nucleus 137mBa, and discuss potential applications of laser-induced caesium-137 decay in radioactive waste disposal.

Barmina, E. V.; Simakin, A. V.; Shafeev, G. A.

2014-08-01

98

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.

2011-07-01

99

Exploring laser-induced interlayer spin transfer by an all-optical method  

NASA Astrophysics Data System (ADS)

We investigate the influence of spin currents during ultrafast laser-induced demagnetization of magnetic bilayer structures by a new all-optical method to measure material- and/or depth-resolved magnetization dynamics. By describing the magneto-optical response of the bilayers in the complex Kerr plane, it is shown that the material-specific magnetization dynamics of the individual layers can be measured by a marginal adjustment to any conventional time-resolved magneto-optical Kerr effect setup. We use this technique to trace superdiffusive spin currents in magnetic Ni/Fe bilayers, providing new insight on its importance to ultrafast laser-induced demagnetization.

Schellekens, A. J.; de Vries, N.; Lucassen, J.; Koopmans, B.

2014-09-01

100

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

2012-06-01

101

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

NASA Astrophysics Data System (ADS)

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 ns, so huge differences in pressure exist in a small area. To prevent measuring the average pressure in a few mm, short FBG with a length of about 0.5mm is developed by Hongkong PolyU and is inserted in the explosive. The light reflected by the FBG is sent to a fibre optic Mach-Zehnder interferometer with a 3x3 beam combiner. Pressure induced wavelength shift will cause a phase change of the interferometric signal. Using the 3 output signals of the interferometer, the phase can be calculated. Interaction between the FBG and the ionization light generated by the shockwave is also demonstrated.

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

2007-01-01

102

Two-dimensional axisymmetric models of laser induced plasmas relevant to laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

A dynamical model of a laser induced plasma with axial symmetry is developed to systematically study the effects of the plasma equation of state, radiation transfer, various transport phenomena (viscosity, thermal conductivity, diffusion), and the ablation surface on the observable quantities such as spectra emitted by LIBS plasmas containing multiple species. Theoretical and numerical foundations of the model are described in detail. It is shown that the plasma spectra simulated with the equation of state based on the energy balance that includes the kinetic (thermal) energy, ionization energy, and energy of electronic excitations in atoms and ions differ significantly from the spectra obtained for plasmas modeled in the ideal gas approximation (where only the kinetic energy is included into the energy balance). Various transport phenomena, such as viscosity, diffusion, and thermal conductivity, are shown to have a little effect on the spectra. Radiation losses are proved to have noticeable effects. The effects of various interactions (adhesion, heat exchange, mass inflows) of the evolving plasma with the ablation surface are also illustrated by numerical simulations for typical LIBS plasmas. The model provides a numerical tool to assess various settings for LIBS plasma experiments as well as to interpret experimental data.

Shabanov, S. V.; Gornushkin, I. B.

2014-10-01

103

Synchronous detection of laser-induced fluorescence  

SciTech Connect

Many toxic or carcinogenic organic molecules have large absorption and fluorescence emission cross sections and can thus be detected by laser-induced fluorescence (LIF) in liquid samples at parts-per-billion levels or better. The technique of synchronous detection of laser-induced fluorescence (SDLIF) provides a way to distinguish between the fluorescence from a toxic molecule and the fluorescence from a background substance. This is done by synchronously scanning the laser excitation and fluorescence detection wavelengths at a fixed wavelength separation. What is measured in the overlap integral of the excitation and emission spectra that is considerably narrower than the entire fluorescence spectrum. The discussion of these techniques is centered on the point and remote detection of polynuclear aromatic hydrocarbons, aromatic amines, and organophosphates having applications in certain manufacturing processes as well as in coal liquefaction and gasification plants.

Quigley, G.P.

1982-01-01

104

Laser-induced surface and coating damage  

Microsoft Academic Search

Results from experiments on laser-induced damage to surfaces of optically polished glass and fused-silica and thin-film coatings are presented. Measurements were made under proper conditions to characterize actual laser components. Data are given for distributions of thresholds for 1.06 micron, 1 ns pulses, the influence of coating materials and designs, and effects of surface preparation on damage threshold, variations of

W. H. Lowdermilk; D. Milam

1981-01-01

105

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

106

[Study of self-absorption effect on laser-induced metal plasma].  

PubMed

In order to reduce the effect of the spectral line self-absorption on the analysis result in the laser induced plasma and enhance the qualities of spectrum, the spectral information was recorded by the spectral analysis system consisting of a modular multifunctional grating spectrometer and a CCD detector etc., and the electron temperature and electron density of the plasma were measured with the spectroscopic methods. A plane mirror device was used to constraint the laser plasma, and a reasonable explanation was got through comparing the linear evolution under different experimental conditions and measuring the temperature, electronic density and sample evaporation. The result shows that when an appropriate plane mirror device was used to constraint the laser plasma, the axial temperature of the plasma increased and the radial distribution of the plasma becomes uniform; the electron density increased dramatically; however, obviously sample evaporation decreased, which may be the reasons for being able to effectively reduce the level of self-absorption spectral lines. Therefore, the plane mirror device could reduce the self-absorption effect in the laser-induced plasma. This makes it possible to choose a sensitive line that acts as analysis line in the quantitative analysis of the major elements. In other words, this promotes the measurement precision in the laser-induced break-down spectroscopy. PMID:25532321

Chen, Jin-Zhong; Ma, Rui-Ling; Wang, Jing; Li, Xu; Su, Hong-Xin

2014-09-01

107

Dynamic strain detection using a fiber Bragg grating sensor array for geotechnical applications  

NASA Astrophysics Data System (ADS)

In recent years fiber Bragg gratings have been successfully introduced as sensors for strain, temperature and pressure variations. Their performance and reliability has been proven in many practical applications including strain monitoring in civil engineering and tunneling, downhole monitoring in oil reservoirs and flow assurance monitoring in pipelines. The gratings have great potential to at as true structurally integrated sensor elements. They can be embedded in typical structural or reinforcing elements of civil and geotechnical buildings. Several methods of interrogation schemes are established depending on the desired accuracy and resolution of the measurement. The most important methods are the linear discriminator, the tunable Fbry-Perot filter technique, and several interferometer setups.

Schmidt-Hattenberger, Cornelia; Naumann, M.; Borm, Gunter

2003-03-01

108

Classical model for laser-induced nonadiabatic collision processes  

NASA Astrophysics Data System (ADS)

By synthesizing earlier work of Orel and Miller and of Meyer, McCurdy, and Miller, a model for describing laser-induced electronically nonadiabatic collision processes is constructed which treats all degrees of freedom—heavy particle (i.e., translation, rotation, and vibration) electronic, and photon—by classical mechanics. This then makes it relatively easy to carry out calculations to simulate such processes within a dynamically consistent framework. Application is made to the test case H+LiF?Li+HF reaction considered by Light and Altenberger-Siczek. The most interesting feature revealed by these classical calculations is maxima in the reaction probability as a function of initial translational energy at energies below the laser-free threshold. It is seen that this structure can be understood as a Franck-Condon-like effect.

Orel, Ann E.; Miller, William H.

1980-07-01

109

Microfabrication of polystyrene microbead arrays by laser induced forward transfer  

NASA Astrophysics Data System (ADS)

In this study we describe a simple method to fabricate microarrays of polystyrene microbeads (PS-?beads) on Thermanox coverslip surfaces using laser induced forward transfer (LIFT). A triazene polymer layer which acts as a dynamic release layer and propels the closely packed microspheres on the receiving substrate was used for this approach. The deposited features were characterized by optical microscopy, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. Ultrasonication was used to test the adherence of the transferred beads. In addition, the laser ejection of the PS-?bead pixels was investigated by time resolved shadowgraphy. It was found that stable PS-?beads micropatterns without any specific immobilization process could be realized by LIFT. These results highlight the increasing role of LIFT in the development of biomaterials, drug delivery, and tissue engineering.

Palla-Papavlu, Alexandra; Dinca, Valentina; Paraico, Iurie; Moldovan, Antoniu; Shaw-Stewart, James; Schneider, Christof W.; Kovacs, Eugenia; Lippert, Thomas; Dinescu, Maria

2010-08-01

110

Laser-induced image technology (yesterday, today, and tomorrow)  

NASA Astrophysics Data System (ADS)

Methods and systems of laser-induced image technology and ways of their development are discussed. These methods depend on kind of laser-induced etch points (marks), which are used for image creation. Today, the marks, which are usually used for this purpose, are laser-induced damages which are a result of breakdown phenomena. The ways for increasing quality of such images are discussed. However, there are also other marks appearing as a result of interaction of power laser radiation with transparent material. The use of these marks opens new opportunities for creation of laser-induced images with special characteristics. These opportunities are also subject of our discussion.

Troitski, Igor

2005-03-01

111

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

112

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

113

Laser induced fluorescence spectroscopy of boron carbide  

NASA Astrophysics Data System (ADS)

Laser induced fluorescence spectrum of boron carbide (BC) between 490 and 560 nm has been recorded and analyzed. Gas-phase BC molecule was produced by the reaction of diborane and methane in the presence of magnesium atom from laser ablation process. The (0, 0), (1, 0), and (2, 0) bands of the B 4? - - X 4? - transition were rotationally analyzed. Spectra of both isotopes: 10BC and 11BC were analyzed. Equilibrium molecular constants for the B 4? - and the X 4? - states for both isotopes were determined.

Ng, Y. W.; Pang, H. F.; Cheung, A. S.-C.

2011-06-01

114

Vibration detection using dynamic photorefractive gratings in KTN\\/KLTN crystals  

Microsoft Academic Search

We demonstrate a sensitive, all-optical, self-aligning holographic microphone\\/vibration sensor utilizing the zero external electric field photorefractive (Zefpr) effect. The device relies on the unique phase relationship, phi = 0, between a spatially periodic intensity standing wave and the resultant index grating created with the Zefpr effect. Under this zero phase condition, the transmitted intensity of interfering beams in a two

Rudolf Hofmeister; Amnon Yariv

1992-01-01

115

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

116

NIR fibre Bragg grating as dynamic sensor: an application of 1D digital wavelet analysis for signal denoising  

NASA Astrophysics Data System (ADS)

During the past decade, many successful studies have evidently shown remarkable capability of Fiber Bragg Gratings (FBG) sensor for dynamic sensing. Most of the research works utilized the 1550 nm wavelength range of FBG sensors. However near infra-red (NIR) FBG sensors can offer the lower cost of Structural health Monitoring (SHM) systems which uses cheaper silicon sources and detectors. Unfortunately, the excessive noise levels that experienced in NIR wavelengths have caused the rejection of sensor that operating in this range of wavelengths for SHM systems. However, with the appropriate use of signal processing tools, these noisy signals can be easily `cleaned'. Wavelet analysis is one of the powerful signal processing tools nowadays, not only for time-frequency analysis but also for signal denoising. This present study revealed that the NIR FBG range gave good response to impact signals. Furthermore, these `noisy' signals' response were successfully filtered using one dimensional wavelet analysis.

Hafizi, Z. M.; Kahandawa, G. C.; Epaarachchi, J.; Lau, K. T.; Canning, J.; Cook, K.

2013-08-01

117

Laser Induced Fluorescence Spectroscopy of Scandium Monoiodide  

NASA Astrophysics Data System (ADS)

The laser induced fluorescence spectrum of scandium monoiodide (ScI) between 787 and 814 nm has been recorded. ScI molecule was produced by reacting laser vaporized Sc atoms with methyl iodide (CH3I). Spectra of eleven vibrational bands of the C1 ?+ - X1 ?+ transition of ScI were obtained and analyzed. A merged least-squares fit of the measured line positions yielded accurate molecular constants for the upper levels of the C1 ?+ state and the v = 1 - 4 levels of the X1 ?+state. One vibrational band observed at 11627 cm-1 belongs to a sub-band transition of the a3 ? state, which is found to be perturbed by the X1 ?+ state. Details of the perturbation and molecular constants obtained will be reported.

Liao, Zhenwu; Yang, Mei; Chan, Man-Chor; Xia, Ye; Cheung, A. S.-C.

2012-06-01

118

Laser induced fluorescence spectroscopy of ruthenium monoboride  

NASA Astrophysics Data System (ADS)

Laser induced fluorescence spectrum of ruthenium monoboride (RuB) in the visible region between 500 and 575 nm was studied. RuB molecule was produced by reacting laser ablated ruthenium atom with 0.5% diborane (B2H6) seeded in argon. Three transition bands of the [18.4]2.5-X2?5/2 transition were recorded and rotationally analyzed. The ground state symmetry and bond length, ro, were determined to be X2?5/2 state and 1.7099 Å, respectively, which is consistent with a 2?i state predicted from electronic configuration using a molecular orbital energy level diagram. This work represents the first experimental investigation of the spectrum of the RuB molecule.

Wang, Na; Ng, Y. W.; Cheung, A. S.-C.

2012-09-01

119

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

120

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

121

Femtosecond laser-induced subwavelength ripples on Al, Si, CaF2 and CR-39  

NASA Astrophysics Data System (ADS)

The formation of self-organized subwavelength ripples on Al, Si, CaF2 and CR-39 induced by 25 fs laser pulses at central wavelength of 800 nm has been observed under certain experimental conditions. In case of Al subwavelength gratings with periodicities ranging from 20 to 220 nm are reported. For CaF2 the periodicity goes up to 625 nm. In case of Si, nano-gratings have the periodicity of 10-100 nm. The interspacing of these gratings is 60 nm in case of CR-39. These features which are significantly shorter than incident laser wavelength are observed at the irradiation fluence slightly higher than the ablation threshold regardless of the target material. In addition to these nanoripples, classical or microripples with an average spacing of 1-2 ?m have also been registered on irradiated surfaces of Al and Si. These microripples have appeared at fluence higher than that is required for nanoripple-formation. It has been found that the formation of the laser-induced ripples is strongly dependent and quite sensitive to the incident laser fluence and the selection of material.

Bashir, Shazia; Shahid Rafique, M.; Husinsky, Wolfgang

2012-03-01

122

Analysis of deposited layers on plasma facing components by laser-induced breakdown spectroscopy: Towards ITER tritium inventory diagnostics  

Microsoft Academic Search

Because of the necessity of tritium inventory diagnostics in the framework of ITER, laser-induced breakdown spectroscopy (LIBS) is under development to analyse the deposited layers on plasma facing components. By means of a fast imaging technique, the time evolutions of the plume intensity and size are investigated. Time- and space-resolved optical emission spectroscopy is applied to characterize the expansion dynamics

L. Mercadier; J. Hermann; C. Grisolia; A. Semerok

2011-01-01

123

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

124

Lateral self-limitation in the laser-induced oxidation of ultrathin metal films  

NASA Astrophysics Data System (ADS)

cw-laser-induced local oxidation of ultrathin (3-60 nm) titanium films on glass in air is studied. It is shown, that the brightening of the films upon through-oxidation forms a negative feedback to this highly nonlinear process. It offers the possibility of stable writing of oxide line structures narrower than the diffraction limited focused laser spot. The optimum metal film thickness is of the order of the light absorption length in the metal. Transparent isolated oxide lines and gratings with periods down to 250 nm and line width down to 165 nm were recorded in 6-15 nm thick Ti films on glass by using the radiation of the Ar ion laser (?=488, 514 nm).

Gorbunov, A. A.; Eichler, H.; Pompe, W.; Huey, B.

1996-11-01

125

Self-limitation of laser-induced thermochemical reactions in ultrathin films  

NASA Astrophysics Data System (ADS)

Lateral self-limitation of the cw-laser-induced local oxidation of ultrathin (3-60 nm) titanium films in air is studied. It is shown, that the brightening of the films on transparent substrate upon through-oxidation forms a negative feedback to this highly-nonlinear process allowing stable writing of transparent oxide line structures narrower than the diffraction limited focused laser spot. The optimum metal film thickness to obtain the greatest optical contrast with the highest resolution is of the order of the light adsorption length in the metal. Transparent isolated oxide lines and gratings with periods down to 250 nm and line width down to 165 nm were recorded in 6 - 15 nm thick Ti films on glass by using the radiation of the Ar ion laser (lambda equals 488, 514 nm).

Gorbunov, Andre A.; Eichler, H.; Pompe, Wolfgang; Huey, B.; Bonnell, D. A.; Akhsakhalyan, A. D.

1997-04-01

126

Superhydrophobic and colorful copper surfaces fabricated by picosecond laser induced periodic nanostructures  

NASA Astrophysics Data System (ADS)

In this study, functional copper surfaces combined with vivid structural colors and superhydrophobicity were fabricated by picosecond laser. Laser-induced periodic surface structures (LIPSS), i.e. ripples, were fabricated by picosecond laser nanostructuring to induce rainbow-like structural colors which are uniquely caused by the grating - type structure. The effects of laser processing parameters on the formation of ripples were investigated. We also discussed the formation mechanism of ripples. With different combinations of the laser processing parameters, ripples with various morphologies were fabricated. After the modification with triethoxyoctylsilane, different types of ripples exhibited different levels of wettability. The fine ripples with minimal redeposited nanoparticles exhibited high adhesive force to water. The increased amount of nanoscale structures decreased the adhesive force to water and increased the contact angle simultaneously. In particular, a specific type of ripples exhibited superhydrophobicity with a large contact angle of 153.9 ± 3.2° and a low sliding angle of 11 ± 3°.

Long, Jiangyou; Fan, Peixun; Zhong, Minlin; Zhang, Hongjun; Xie, Yongde; Lin, Chen

2014-08-01

127

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

128

Improved Imaging With Laser-Induced Eddy Currents  

NASA Technical Reports Server (NTRS)

System tests specimen of material nondestructively by laser-induced eddy-current imaging improved by changing method of processing of eddy-current signal. Changes in impedance of eddy-current coil measured in absolute instead of relative units.

Chern, Engmin J.

1993-01-01

129

Laser-induced plasma spectroscopy: principles, methods and applications  

SciTech Connect

Principles of the Laser Induced Plasma Spectroscopy and its advances are reported. Methods for obtaining quantitative analyses are described, together with discussion of some applications and the specific problems.

Lazic, Violeta; Colao, Francesco; Fantoni, Roberta; Spizzichino, Valeria [ENEA, FIS-LAS, V. E. Fermi 45, Frascati (RM) (Italy); Jovicevic, Sonja [Institute of Physics, 11080 Belgrade, Pregrevica 118 (Serbia and Montenegro)

2006-12-01

130

Spectral and Dynamic Characteristics of Helium Plasma Emission and its Effect on a Laser-Ablated Target Emission in a Double-Pulse Laser-Induced Breakdown Spectroscopy (LIBS) Experiment.  

PubMed

A systematic study has been performed on the spectral characteristics of the full spectrum of He emission lines and their time-dependent behaviors measured from the He gas plasmas generated by a nanosecond neodymium-doped yttrium aluminum garnet laser. It is shown that among the major emission lines observed, the triplet He(I) 587.6 nm emission line stands out as the most prominent and long-lasting line, associated with de-excitation of the metastable triplet (S = 1) excited state (1s(1) 3d(1)). The role of this metastable excited state is manifested in the intensity enhancement and prolonged life time of the Cu emission with narrow full width half-maximum, as demonstrated in an orthogonal double-pulse experiment using a picosecond laser for the target ablation and a nanosecond laser for the prior generation of the ambient He gas plasma. These desirable emission features are in dire contrast to the characteristics of emission spectra observed with N2 ambient gas having no metastable excited state, which exhibit an initial Stark broadening effect and rapid intensity diminution typical to thermal shock wave-induced emission. The aforementioned He metastable excited state is therefore responsible for the demonstrated favorable features. The advantage of using He ambient gas in the double-pulse setup is further confirmed by the emission spectra measured from a variety of samples. The results of this study have thus shown the potential of extending the existing laser-induced breakdown spectroscopy application to high-sensitivity and high-resolution spectrochemical analysis of wide-ranging samples with minimal destructive effect on the sample surface. PMID:25506688

Jobiliong, Eric; Suyanto, Hery; Marpaung, Alion Mangasi; Abdulmadjid, Syahrun Nur; Idris, Nasrullah; Hedwig, Rinda; Ramli, Muliadi; Pardede, Marincan; Suliyanti, Maria Margaretha; Kagawa, Kiichiro; Fukumoto, Ken-Ichi; Tjia, May On; Lie, Tjung Jie; Lie, Zener Sukra; Kurniawan, Koo Hendrik

2015-01-01

131

Laser-induced fluorescence of CN in solid propellant flames  

SciTech Connect

This paper discusses the application of laser-induced fluorescence of the CN radical as a combustion diagnostic probe for solid propellant flames at pressure up to 3.5 MPa. The key to mitigating severe interference from Mie scattering and other laser-induced effects is that the observed fluorescence wavelength in the CN 0,0 band is well removed spectrally from the laser wavelength (coinciding with the CN 0,1 bandhead).

Edwards, T.; Weaver, D.P.; Campbell, D.H.; Frederick, F.

1986-01-01

132

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

133

Laser induced damage studies in mercury cadmium telluride  

NASA Astrophysics Data System (ADS)

We have investigated laser induced damage at 1.06 ?m laser wavelength in diamond paste polished (mirror finish) and carborundum polished Hg0.8Cd0.2Te (MCT) samples with increasing fluence as well as number of pulses. Evolution of damage morphology in two types of samples is quite different. In case of diamond paste polished samples, evolution of damage morphological features is consistent with Hg evaporation with transport of Cd/Te globules towards the periphery of the molten region. Cd/Te globules get accumulated with successive laser pulses at the periphery indicating an accumulation effect. Real time reflectivity (RTR) measurement has been done to understand melt pool dynamics. RTR measurements along with the thermal profile of the melt pool are in good agreement with thermal melting model of laser irradiated MCT samples. In case of carborundum polished samples, laser damage threshold is significantly reduced. Damage morphological features are significantly influenced by surface microstructural condition. From comparison of the morphological features in the two cases, it can be inferred that laser processing of MCT for device applications depends significantly on surface preparation conditions.

Garg, Amit; Kapoor, Avinashi; Tripathi, K. N.; Bansal, S. K.

2007-10-01

134

Femtosecond laser-induced periodic surface structures on silica  

SciTech Connect

The formation of laser-induced periodic surface structures (LIPSS) on two different silica polymorphs (single-crystalline synthetic quartz and commercial fused silica glass) upon irradiation in air with multiple linearly polarized single- and double-fs-laser pulse sequences ({tau} = 150 fs pulse duration, {lambda} = 800 nm center wavelength, temporal pulse separation {Delta}t < 40 ps) is studied experimentally and theoretically. Two distinct types of fs-LIPSS [so-called low-spatial-frequency LIPSS (LSFL) and high-spatial-frequency LIPSS (HSFL)] with different spatial periods and orientations were identified. Their appearance was characterized with respect to the experimental parameters peak laser fluence and number of laser pulses per spot. Additionally, the 'dynamics' of the LIPSS formation was addressed in complementary double-fs-pulse experiments with varying delays, revealing a characteristic change of the LSFL periods. The experimental results are interpreted on the basis of a Sipe-Drude model considering the carrier dependence of the optical properties of fs-laser excited silica. This new approach provides an explanation of the LSFL orientation parallel to the laser beam polarisation in silica - as opposed to the behaviour of most other materials.

Hoehm, S.; Rosenfeld, A. [Max-Born-Institut fuer Nichtlineare Optik und Kurzzeitspektroskopie (MBI), Max-Born-Strasse 2A, D-12489 Berlin (Germany); Krueger, J.; Bonse, J. [BAM Bundesanstalt fuer Materialforschung und-pruefung, Unter den Eichen 87, D-12205 Berlin (Germany)

2012-07-01

135

Multiple fiber Bragg grating sensor network with a rapid response and wide spectral dynamic range using code division multiple access  

NASA Astrophysics Data System (ADS)

Fiber Bragg grating (FBG) sensor networks have been intensively researched in optical sensor area and it developed in wavelength division multiplexing (WDM) and time division multiplexing (TDM) technologies which was adopted for its interrogating many optical sensors. In particular, WDM technology can be easily employed to interrogate FBG sensor however, the number of FBG sensors is limited. On the other hand, the TDM technique can extremely expand the number of sensor because the FBG sensors have same center wavelength. However, it suffers from a reduced sensor output power due to low reflectivity of FBG sensor. In this paper, we proposed and demonstrated the FBG sensor network based on code division multiple access (CDMA) with a rapid response and wide spectral dynamic range. The reflected semiconductor optical amplifier (RSOA) as a light source was directly modulated by the generated pseudorandom binary sequence (PRBS) code and the modulated signal is amplified and goes through FBG sensors via circulator. When the modulated optical signal experienced FBG sensor array, the optical signal which was consistent with center wavelength of FBGs is reflected and added from each sensors. The added signal goes into dispersion compensating fiber (DCF) as a dispersion medium. After through the DCF, the optical signal is converted into electrical signal by using photodetector (PD). For separate individual reflected sensor signal, the sliding correlation method was used. The proposed method improves the code interference and it also has advantages such as a large number of sensors, continuously measuring individual sensors, and decreasing the complexity of the sensor network.

Kim, Youngbok; Jeon, Sie-Wook; Park, Chang-Soo

2011-05-01

136

Interfacial Effects in the Relaxation Dynamics of Silver Nanometal-Glass Composites Probed by Transient Grating Spectroscopy  

NASA Astrophysics Data System (ADS)

Relaxation dynamics of silver nanoparticles (NPs) embedded in glass have been studied by picosecond time-resolved transient grating (TG) spectroscopy. Phosphate-based glasses were prepared by melting and heat-treatment processes by which two different nanometal-glass composites were produced. The first is a glass system containing silver and tin in which Ag NPs are embedded in the matrix upon heat treatment. The second is a heat-treated silver-doped glass with spectroscopic indications of Ag+-Ag0 pairs located at or near the surface of the NPs. The time evolution of the light-induced TG for the Ag/Sn-doped glass shows an uncommon relaxation on the nanosecond time scale. Such behavior is explained in terms of energy transfer processes between polaronic and/or excitonic states in the near-interface region of the glass matrix and the NPs. In contrast, a faster monotonic relaxation is observed for the Ag-doped nanocomposite. This result is attributed to Ag NP ? Ag+-Ag0 plasmon resonance energy transfer.

Jiménez, J. A.; Lysenko, S.; Vikhnin, V. S.; Liu, H.

2010-01-01

137

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

138

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

SciTech Connect

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. [CIC microGUNE, Goiru Kalea 9 Polo Innovación Garaia, 20500 Arrasate-Mondragón (Spain); CEIT-IK4 and Tecnun, University of Navarra, Manuel Lardizábal 15, 20018 San Sebastián (Spain); Rodriguez, A. [CIC microGUNE, Goiru Kalea 9 Polo Innovación Garaia, 20500 Arrasate-Mondragón (Spain)

2014-05-07

139

Laser-Induced-Fluorescence Photogrammetry and Videogrammetry  

NASA Technical Reports Server (NTRS)

An improved method of dot-projection photogrammetry and an extension of the method to encompass dot-projection videogrammetry overcome some deficiencies of dot-projection photogrammetry as previously practiced. The improved method makes it possible to perform dot-projection photogrammetry or videogrammetry on targets that have previously not been amenable to dot-projection photogrammetry because they do not scatter enough light. Such targets include ones that are transparent, specularly reflective, or dark. In standard dot-projection photogrammetry, multiple beams of white light are projected onto the surface of an object of interest (denoted the target) to form a known pattern of bright dots. The illuminated surface is imaged in one or more cameras oriented at a nonzero angle or angles with respect to a central axis of the illuminating beams. The locations of the dots in the image(s) contain stereoscopic information on the locations of the dots, and, hence, on the location, shape, and orientation of the illuminated surface of the target. The images are digitized and processed to extract this information. Hardware and software to implement standard dot-projection photogrammetry are commercially available. Success in dot-projection photogrammetry depends on achieving sufficient signal-to-noise ratios: that is, it depends on scattering of enough light by the target so that the dots as imaged in the camera(s) stand out clearly against the ambient-illumination component of the image of the target. In one technique used previously to increase the signal-to-noise ratio, the target is illuminated by intense, pulsed laser light and the light entering the camera(s) is band-pass filtered at the laser wavelength. Unfortunately, speckle caused by the coherence of the laser light engenders apparent movement in the projected dots, thereby giving rise to errors in the measurement of the centroids of the dots and corresponding errors in the computed shape and location of the surface of the target. The improved method is denoted laser-induced-fluorescence photogrammetry.

Danehy, Paul; Jones, Tom; Connell, John; Belvin, Keith; Watson, Kent

2004-01-01

140

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

141

Laser-induced thermal acoustic velocimetry  

NASA Astrophysics Data System (ADS)

Laser-Induced Thermal Acoustics (LITA) is a non- intrusive, remote, four-wave mixing laser diagnostic technique for measurements of the speed of sound and of the thermal diffusivity in gases. If the gas composition is known, then its temperature and density can be inferred. Beam misalignments and bulk fluid velocities can influence the time history and intensity of LITA signals. A closed-form analytic expression for LITA signals incorporating these effects is derived. The magnitude of beam misalignment and the flow velocity can be inferred from the signal shape using a least-squares fit of this model to the experimental data. High-speed velocimetry using homodyne detection is demonstrated with NO2-seeded air in a supersonic blow-down nozzle. The measured speed of sound deviates less than 2% from the theoretical value assuming isentropic quasi-1D flow. Boundary layer effects degrade the velocity measurements to errors of 20%. Heterodyne detection is used for low-speed velocimetry up to Mach number M = 0.1. The uncertainty of the velocity measurements was ~0.2 m/s. The sound speed measurements were repeatable to 0.5%. The agreement between theory and experiments is very good. A one-hidden-layer feed-forward neural network is trained using back-propagation learning and a steepest descent learning rule to extract the speed of sound and flow velocity from a heterodyne LITA signal. The effect of the network size on the performance is demonstrated. The accuracy is determined with a second set of LITA signals that were not used during the training phase. The accuracy is found to be better than that of a conventional frequency decomposition technique while being computationally as efficient. This data analysis method is robust with respect to noise, numerically stable, and fast enough for real-time data analysis. The accuracy and uncertainty of non-resonant LITA measurements is investigated. The error in measurements of the speed of sound and of the thermal diffusivity initially decreases with increasing signal intensity (excitation beam pulse energy) and increases again after passing a minimum. The location of the minimum error for the speed of sound and for the thermal diffusivity coincide. The errors at the minimum are 0.03% and 1%, respectively. The uncertainties for the speed of sound and the thermal diffusivity decrease monotonically to 0.25% and 5%, respectively. The increased error for high excitation beam pulse energies results from finite- strength waves that cannot be treated using the linearized equations of motion.

Schlamp, Stefan

2000-11-01

142

Laser-induced differential normalized fluorescence method for cancer diagnosis  

DOEpatents

An apparatus and method for cancer diagnosis are disclosed. The diagnostic method includes the steps of irradiating a tissue sample with monochromatic excitation light, producing a laser-induced fluorescence spectrum from emission radiation generated by interaction of the excitation light with the tissue sample, and dividing the intensity at each wavelength of the laser-induced fluorescence spectrum by the integrated area under the laser-induced fluorescence spectrum to produce a normalized spectrum. A mathematical difference between the normalized spectrum and an average value of a reference set of normalized spectra which correspond to normal tissues is calculated, which provides for amplifying small changes in weak signals from malignant tissues for improved analysis. The calculated differential normalized spectrum is correlated to a specific condition of a tissue sample. 5 figs.

Vo-Dinh, T.; Panjehpour, M.; Overholt, B.F.

1996-12-03

143

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

144

Laser-induced differential normalized fluorescence method for cancer diagnosis  

DOEpatents

An apparatus and method for cancer diagnosis are disclosed. The diagnostic method includes the steps of irradiating a tissue sample with monochromatic excitation light, producing a laser-induced fluorescence spectrum from emission radiation generated by interaction of the excitation light with the tissue sample, and dividing the intensity at each wavelength of the laser-induced fluorescence spectrum by the integrated area under the laser-induced fluorescence spectrum to produce a normalized spectrum. A mathematical difference between the normalized spectrum and an average value of a reference set of normalized spectra which correspond to normal tissues is calculated, which provides for amplifying small changes in weak signals from malignant tissues for improved analysis. The calculated differential normalized spectrum is correlated to a specific condition of a tissue sample.

Vo-Dinh, Tuan (Knoxville, TN); Panjehpour, Masoud (Knoxville, TN); Overholt, Bergein F. (Knoxville, TN)

1996-01-01

145

Ultrafast molecular imaging by laser-induced electron diffraction  

SciTech Connect

We address the feasibility of imaging geometric and orbital structures of a polyatomic molecule on an attosecond time scale using the laser-induced electron diffraction (LIED) technique. We present numerical results for the highest molecular orbitals of the CO{sub 2} molecule excited by a near-infrared few-cycle laser pulse. The molecular geometry (bond lengths) is determined within 3% of accuracy from a diffraction pattern which also reflects the nodal properties of the initial molecular orbital. Robustness of the structure determination is discussed with respect to vibrational and rotational motions with a complete interpretation of the laser-induced mechanisms.

Peters, M. [Universite Paris-Sud, Institut des Sciences Moleculaires d'Orsay (CNRS), F-91405 Orsay (France); Departement de Chimie, Universite Laval, Quebec, Quebec G1K 7P4 (Canada); Nguyen-Dang, T. T. [Departement de Chimie, Universite Laval, Quebec, Quebec G1K 7P4 (Canada); Cornaggia, C. [CEA IRAMIS, SPAM, Saclay, Batiment 522, F-91191 Gif-sur-Yvette (France); Saugout, S.; Charron, E.; Keller, A.; Atabek, O. [Universite Paris-Sud, Institut des Sciences Moleculaires d'Orsay (CNRS), F-91405 Orsay (France)

2011-05-15

146

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

147

Ultrafast Molecular Imaging by Laser Induced Electron Diffraction  

E-print Network

We address the feasibility of imaging geometric and orbital structure of a polyatomic molecule on an attosecond time-scale using the laser induced electron diffraction (LIED) technique. We present numerical results for the highest molecular orbitals of the CO2 molecule excited by a near infrared few-cycle laser pulse. The molecular geometry (bond-lengths) is determined within 3% of accuracy from a diffraction pattern which also reflects the nodal properties of the initial molecular orbital. Robustness of the structure determination is discussed with respect to vibrational and rotational motions with a complete interpretation of the laser-induced mechanisms.

Michel Peters; Tung Nguyen-Dang; Christian Cornaggia; Sébastien Saugout; Eric Charron; Arne Keller; Osman Atabek

2010-09-29

148

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

149

Aspects of Laser Induced Fluorescence Employing Pulsed and Modulated Excitation  

NASA Astrophysics Data System (ADS)

This work reports on various aspects of employing strong, pulsed or modulated excitation in laser induced fluorescence (LIF) experiments. Part I is motivated by two-photon LIF measurements in nitric oxide, used for the determination of temperatures and concentrations in cold flows. It is found that dynamical Stark effects modify the lineshapes of individual rotational transitions significantly, thereby invalidating conventional methods of data analysis. It is shown that, to maintain calibration, one must extract the true intensity dependence of the underlying nonlinear interactions from data that are spatially and temporally unresolved. This inversion problem is developed and solved for nonsaturated as well as saturated excitation, namely by the use of Abel inversion, moment expansion, and collocation in terms of kernel or spline basis functions. Further applications of these techniques to problems in laser diagnostics are discussed. Part II is concerned with fundamental aspects of a proposed laser fluorescence velocimeter. In this instrument, flow velocities are derived from the depth -of-modulation or the phase-shift of the fluorescence signal with respect to the bichromatic (fully amplitude modulated) input field. By solving the pertinent Bloch equations it is found that, unlike for weak excitation, the inhomogeneously broadened response of such a system deviates considerably from that of a similar system driven by a broadband field. Thus, conventional results from phase-sensitive fluorometry are inapplicable. Instead, much insight can be gained from the concepts of multiple quantum resonances and Bloch-Siegert shifts, taken from magnetic resonance. However, this work moves beyond merely transferring these concepts to optical resonance, in particular by studying the behavior of harmonic interaction components. Also, it is discussed how similar insights can be applied to other optical interactions, for example those involving phase-modulation.

Ruyten, Wilhelmus M. J.

150

Airborne simultaneous spectroscopic detection of laser-induced water Raman backscatter and fluorescence from chlorophyll a and other naturally occurring pigments  

NASA Technical Reports Server (NTRS)

The airborne laser-induced spectral emission bands obtained simultaneously from water Raman backscatter and the fluorescence of chlorophyll and other naturally occurring waterborne pigments are reported here for the first time. The importance of this type data lies not only in its single-shot multispectral character but also in the application of the Raman line for correction or calibration of the spatial variation of the laser penetration depth without the need for in situ water attenuation measurements. The entire laser-induced fluorescence and Raman scatter emissions resulting from each separate 532-nm 10-nsec laser pulse are collected and spectrally dispersed in a diffraction grating spectrometer having forty photomultiplier tube detectors. Results from field experiments conducted in the North Sea and the Chesapeake Bay/Potomac River are presented. Difficulties involving the multispectral resolution of the induced emissions are addressed, and feasible solutions are suggested together with new instrument configurations and future research directions.

Hoge, F. E.; Swift, R. N.

1981-01-01

151

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

152

Laser-Induced Fluorescence in plasmas at UC Irvine  

Microsoft Academic Search

For about 25 years laser-induced fluorescence (LIF) has been performed at UC Irvine with many people contributing over that time period. A central contributor to the work has been Raul Stern, whether directly involved with the experiments at hand or via physics advice obtained wherever he could be found worldwide spreading the joys of LIF. At Irvine LIF has been

R. McWilliams

2003-01-01

153

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 thermometry in shock tube flow fields using toluene as a fluorescence tracer in nitrogen. Fluorescence quantum yield values needed to quantify PLIF images were measured in a static cell at low pressures (<1 bar) for various toluene partial pressures in nitrogen bath gas. Images

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

2010-01-01

154

Laser induced desorption as tritium retention diagnostic method in ITER  

Microsoft Academic Search

Measurement and control of long term tritium retention is one of the most critical issues for ITER and future fusion devices. Since the measurement of the hydrogenic retention by post mortem tile analysis becomes more and more difficult in future devices due to active water cooling and tile activation, Laser Induced Desorption Spectroscopy (LIDS) is under development in TEXTOR to

M. Zlobinski; V. Philipps; B. Schweer; A. Huber; S. Brezinsek; Ch. Schulz; S. Möller; U. Samm

2011-01-01

155

Infrared Laser-Induced Breakdown Spectroscopy of Alkali Metal Halides  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) is a powerful diagnostic tool for detection of trace elements by monitoring the atomic and ionic emission from laser-induced plasmas. LIBS is a relatively simple technique and has been successfully employed in applications such as environmental monitoring, materials analysis, medical diagnostics, industrial process control, and homeland security. Most LIBS applications are limited to emission features in the ultraviolet-visible-near infrared (UV-VIS-NIR) region arising from atoms and simple molecular fragments. In the present work, we report on the observation of mid- infrared emission lines from alkali metal halides due to laser-induced breakdown processes. The studied alkali metal halides included LiCl, NaCl, NaBr, KCl, KBr, KF, RbCl, and RbBr. The laser-induced plasma was produced by focusing a 16 mJ pulsed Nd:YAG laser (1064 nm) on the target. The LIBS infrared emission from alkali halides showed intense and narrow bands located in the region from 2-8 ?m. The observed emission features were assigned to atomic transitions between higher-lying Rydberg states of neutral alkali atoms. More detailed results of the performed IR LIBS studies on alkali metal halides will be discussed at the conference.

Brown, Ei; Hommerich, Uwe; Yang, Clayton; Trivedi, Sudhir; Samuels, Alan; Snyder, Peter

2008-10-01

156

Laser-Induced Kerr Constants for Pure Liquids  

Microsoft Academic Search

During the past two decades an increasing number of publications have reported laser-induced birefringence data for pure liquids. To date there has been no comparative collection of values from these experiments. This paper lists the published values together with hitherto unpublished data of the authors of the optically induced Kerr constant B0. The normalized parameter Brel for data compared with

N. J. Harrison; B. R. Jennings

1992-01-01

157

Laser-Induced Mouse Model of Chronic Ocular Hypertension  

E-print Network

) is considered a primary risk factor for the initiation and progression of glaucomatous neuropathy.2 However human diseases could provide an opportunity to identify possible risk factors that may predispose to andLaser-Induced Mouse Model of Chronic Ocular Hypertension Sinisa D. Grozdanic,1,2 Daniel M. Betts,1

Sakaguchi, Donald S.

158

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

159

Nd:YAG-CO2 double-pulse laser induced breakdown spectroscopy of organic films  

E-print Network

, USA 2 National Center for Forensic Science, University of Central Florida, Orlando, FL, USA 3 optics: Laser-induced breakdown; (160.4890) Organic materials; (300.6365) Spectroscopy, laser induced., and A. W. Miziolek, "Laser-induced breakdown spectroscopy analysis of energetic materials," Appl. Opt

Richardson, Martin C.

160

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

161

IKK2 Inhibition Attenuates Laser-Induced Choroidal Neovascularization  

PubMed Central

Choroidal neovascularization (CNV) is aberrant angiogenesis associated with exudative age-related macular degeneration (AMD), a leading cause of blindness in the elderly. Inflammation has been suggested as a risk factor for AMD. The IKK2/NF-?B pathway plays a key role in the inflammatory response through regulation of the transcription of cytokines, chemokines, growth factors and angiogenic factors. We investigated the functional role of IKK2 in development of the laser-induced CNV using either Ikk2 conditional knockout mice or an IKK2 inhibitor. The retinal neuronal tissue and RPE deletion of IKK2 was generated by breeding Ikk2?/flox mice with Nestin-Cre mice. Deletion of Ikk2 in the retina caused no obvious defect in retinal development or function, but resulted in a significant reduction in laser-induced CNV. In addition, intravitreal or retrobulbar injection of an IKK2 specific chemical inhibitor, TPCA-1, also showed similar inhibition of CNV. Furthermore, in vitro inhibition of IKK2 in ARPE-19 cells significantly reduced heat shock-induced expression of NFKBIA, IL1B, CCL2, VEGFA, PDGFA, HIF1A, and MMP-2, suggesting that IKK2 may regulate multiple molecular pathways involved in laser-induced CNV. The in vivo laser-induced expression of VEGFA, and HIF1A in RPE and choroidal tissue was also blocked by TPCA-1 treatment. Thus, IKK2/NF-?B signaling appears responsible for production of pro-inflammatory and pro-angiogenic factors in laser-induced CNV, suggesting that this intracellular pathway may serve as an important therapeutic target for aberrant angiogenesis in exudative AMD. PMID:24489934

Lu, Huayi; Lu, Qingxian; Gaddipati, Subhash; Kasetti, Ramesh Babu; Wang, Wei; Pasparakis, Manolis; Kaplan, Henry J.; Li, Qiutang

2014-01-01

162

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

163

Interlaced spin grating for optical wave filtering  

E-print Network

Interlaced Spin Grating is a scheme for the preparation of spectro-spatial periodic absorption gratings in a inhomogeneously broadened absorption profile. It relies on the optical pumping of atoms in a nearby long-lived ground state sublevel. The scheme takes advantage of the sublevel proximity to build large contrast gratings with unlimited bandwidth and preserved average optical depth. It is particularly suited to Tm-doped crystals in the context of classical and quantum signal processing. In this paper, we study the optical pumping dynamics at play in an Interlaced Spin Grating and describe the corresponding absorption profile shape in an optically thick atomic ensemble. We show that, in Tm:YAG, the diffraction efficiency of such a grating can reach 18.3% in the small angle, and 11.6% in the large angle configuration when the excitation is made of simple pulse pairs, considerably outperforming conventional gratings.

Héloïse Linget; Thierry Chanelière; Jean-Louis Le Gouët; Perrine Berger; Loïc Morvan; Anne Louchet-Chauvet

2014-07-15

164

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

165

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

166

Quantifying pulsed laser induced damage to graphene  

SciTech Connect

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 sp{sup 2}-carbon bonding structures with optical pulse fluences as low as 14 mJ/cm{sup 2}, 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 [Optical Sciences Division and Electronics Science and Technology Division, Naval Research Laboratory, Washington DC 20375 (United States)

2011-11-21

167

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

168

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

169

Laser-induced incandescence calibration via gravimetric sampling  

NASA Technical Reports Server (NTRS)

Absolute calibration of laser-induced incandescence (LII) is demonstrated via comparison of LII signal intensities with gravimetrically determined soot volume fractions. This calibration technique does not rely upon calculated or measured optical characteristics of soot. The variation of the LII signal with gravimetrically measured soot volume fractions ranging from 0.078 to 1.1 ppm established the linearly of the calibration. With the high spatial and temporal resolution capabilities of laser-induced incandescence (LII), the spatial and temporal fluctuations of the soot field within a gravimetric chimney were characterized. Radial uniformity of the soot volume fraction, f(sub v) was demonstrated with sufficient averaging of the single laser-shot LII images of the soot field thus confirming the validity of the calibration method for imaging applications. As illustration, instantaneous soot volume fractions within a Re = 5000 ethylene/air diffusion flame measured via planar LII were established quantitatively with this calibration.

Choi, M. Y.; Vander Wal, R. L.; Zhou, Z.

1996-01-01

170

Polarization Resolved Laser-Induced Breakdown Spectroscopy of Al  

NASA Astrophysics Data System (ADS)

It is shown that the continuous background of the laser-induced breakdown spectrum of Al produced by 800 nm femtosecond pulses is strongly polarized. Use of a polarizer to filter out the background significantly improves the signal/noise and signal/background ratios of the discrete line spectrum. The effects of the laser pulse energy, focal position, incidence and detection angles, and the polarization plane of the laser were investigated. Polarization resolved laser-induced breakdown spectroscopy (PRLIBS) is much less sensitive to these variables than conventional, ungated fs-LIBS, making this a much more versatile analytical tool. These measurements reveal qualitatively different mechanisms for the continuous and discrete parts of the spectrum.

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

2009-08-01

171

Laser-induced macular holes demonstrate impaired choroidal perfusion  

NASA Astrophysics Data System (ADS)

Choroidal perfusion was evaluated following the creation of a laser induced macular hole in a nonhuman primate model. Two Rhesus monkeys underwent macular exposures delivered by a Q-switched Nd:YAG laser. The lesions were evaluated with fluorescein angiography and indocyanine green (ICG) angiography . Each lesion produced vitreous hemorrhage and progressed to a full thickness macular hole. ICG angiography revealed no perfusion of the choriocapillaris beneath the lesion centers. Histopathologic evaluation showed replacement of the choriocapillaris with fibroblasts and connective tissue. Nd:YAG, laser-induced macular holes result in long term impairment of choroidal perfusion at the base of the hole due to choroidal scarring and obliteration of the choriocapillaris.

Brown, Jeremiah, Jr.; Allen, Ronald D.; Zwick, Harry; Schuschereba, Steven T.; Lund, David J.; Stuck, Bruce E.

2003-06-01

172

Narrowband Fiber Grating Filters  

Microsoft Academic Search

Two techniques for the fabrication of fiber gratings with a narrowband filter response are reported. In the first technique, the reflection bandwidth is reduced by increasing the grating length. Fiber gratings 10 mm long have been made with a bandwidth of ~0.3 nm. In the second technique, a phase shift is incorporated into the grating to form a resonant structure.

Catherine M. Ragdale; Douglas Reid; D. J. Robbins; Jens Buus; Ian Bennion

1990-01-01

173

Laser-induced chemical etching of silicon in chlorine atmosphere  

Microsoft Academic Search

Laser-induced chemical etching of single-crystalline (100) Si in Cl2 atmosphere has been investigated for continuous Ar+ and Kr+ laser irradiation at around 351 nm, and at 457.9, 488.0, 514.5, and 647.1 nm. For laser irradiances below 105 W\\/cm2 the etching mechanism is non-thermal, and is based on photo-generated electron-hole pairs within the Si surface and Cl atoms produced within the

P. Mogyorósi; K. Piglmayer; R. Kullmer; D. Bäuerle

1988-01-01

174

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

175

Vacuum ultraviolet laser-induced breakdown spectroscopy analysis of polymers  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) in the vacuum ultraviolet range (VUV, ?<200nm) is employed for the detection of trace elements in polyethylene (PE) that are difficult to detect in the UV\\/VIS range. For effective laser ablation of PE, we use a F2 laser (wavelength ?=157nm) with a laser pulse length of 20ns, a pulse energy up to 50mJ, and pulse repetition

Juraj Jasik; Johannes Heitz; Johannes D. Pedarnig; Pavel Veis

2009-01-01

176

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

177

Laser-induced fluorescence observations of a multipolar argon discharge  

SciTech Connect

Observations carried out with a laser-induced fluorescence diagnostic on several configurations of a multipolar discharge are presented. This diagnostic allows very accurate measurements of the ion velocity distribution function in the argon plasma and reveals the presence of double-hump velocity distribution functions due to ion acceleration in the static plasma potential and ion reflection on a multipolar magnetic field. These observations give a new insight to ion temperature and ion drifts inside the device.

Bachet, G.; Cherigier, L.; Carrere, M.; Doveil, F. (Equipe Turbulence Plasma de l'URA 773 du CNRS et de l'Universite de Provence, Institut Mediterraneen de Technologie, F13451 Marseille Cedex 13 (France))

1993-08-01

178

UV nanosecond laser-induced birefringence in LBG glasses  

Microsoft Academic Search

In this paper, we present results on UV pulsed laser-induced birefringence in La2O3–B2O3–GeO2 (LBG) glasses. Samples were irradiated at a wavelength of 355?nm delivered by an Nd–YAG laser operating in the nanosecond regime. After irradiation, glasses were analyzed by micro-Raman spectroscopy and small angle X-ray scattering (SAXS). Raman spectra show figures characteristic of a light polarization rotation effect in agreement

D. Vouagner; C. Coussa; V. Califano; C. Martinet; B. Champagnon; V. Sigaev

2007-01-01

179

Si II transition probabilities measurements in a laser induced plasma  

Microsoft Academic Search

SiII lines are observed in a laser-induced plasma, generated by a laser pulse focused on a silicon solid target, in a xenon plus hydrogen atmosphere. They are measured when the plasma reaches local thermal equilibrium (LTE). The spectra is numerically corrected from self-absorption. Transition probabilities of SiII Mult. (1)–(5); (8); (9); (3.01); (7.26) lines are measured, for the two last

P. Matheron; A. Escarguel; R. Redon; A. Lesage; J. Richou

2001-01-01

180

Ultratrace analysis of transuranic actinides by laser-induced fluorescence  

DOEpatents

Ultratrace quantities of transuranic actinides are detected indirectly by their effect on the fluorescent emissions of a preselected fluorescent species. Transuranic actinides in a sample are coprecipitated with a host lattice material containing at least one preselected fluorescent species. The actinide either quenches or enhances the laser-induced fluorescence of the preselected fluorescent species. The degree of enhancement or quenching is quantitatively related to the concentration of actinide in the sample.

Miller, Steven M. (Chelmsford, MA)

1988-01-01

181

Ultratrace analysis of transuranic actinides by laser-induced fluorescence  

DOEpatents

Ultratrace quantities of transuranic actinides are detected indirectly by their effect on the fluorescent emissions of a preselected fluorescent species. Transuranic actinides in a sample are coprecipitated with a host lattice material containing at least one preselected fluorescent species. The actinide either quenches or enhances the laser-induced fluorescence of the preselected fluorescent species. The degree of enhancement or quenching is quantitatively related to the concentration of actinide in the sample.

Miller, S.M.

1983-10-31

182

Coherent microwave radiation from a laser induced plasma  

NASA Astrophysics Data System (ADS)

We propose a method for generation of coherent monochromatic microwave/terahertz radiation from a laser-induced plasma. It is shown that small-scale plasma, located in the interaction region of two co-propagating plane-polarized laser beams, can be a source of the dipole radiation at a frequency equal to the difference between the frequencies of the lasers. This radiation is coherent and appears as a result of the so-called optical mixing in plasma.

Shneider, M. N.; Miles, R. B.

2012-12-01

183

Picosecond electron deflectometry of laser-induced plasmas  

Microsoft Academic Search

We demonstrate a method for real-time imaging of the field distribution in laser-induced plasmas with picosecond temporal resolution. The plasma is generated by a 50 fs laser pulse focused in nitrogen gas jet, and is then probed by a picosecond electron pulse synchronized with the laser. Pump-probe images of the electron beam at different delay times are recorded on a

Martin Centurion; Peter Reckenthaeler; Alexander Apolonskiy; Ferenc Krausz; Ernst Fill

2008-01-01

184

Quantitative ultrasound method to detect and monitor laser-induced cavitation bubbles  

PubMed Central

An ultrasound technique to measure the spatial and temporal behavior of the laser-induced cavitation bubble is introduced. The cavitation bubbles were formed in water and in gels using a nanosecond pulsed Nd:YAG laser operating at 532 nm. A focused, single-element, 25-MHz ultrasound transducer was employed both to detect the acoustic emission generated by plasma expansion and to acoustically probe the bubble at different stages of its evolution. The arrival time of the passive acoustic emission was used to estimate the location of the cavitation bubble’s origin and the time of flight of the ultrasound pulse-echo signal was used to define its spatial extent. The results of ultrasound estimations of the bubble size were compared and found to be in agreement with both the direct optical measurements of the stationary bubble and the theoretical estimates of bubble dynamics derived from the well-known Rayleigh model of a cavity collapse. The results of this study indicate that the proposed quantitative ultrasound technique, capable of detecting and accurately measuring laser-induced cavitation bubbles in water and in a tissue-like medium, could be used in various biomedical and clinical applications. PMID:18601556

Karpiouk, Andrei B.; Aglyamov, Salavat R.; Bourgeois, Frederic; Ben-Yakar, Adela; Emelianov, Stanislav Y.

2008-01-01

185

Fiber optic probe for determining heavy metals in solids based on laser-induced plasmas  

NASA Astrophysics Data System (ADS)

A fiber-optic probe suitable for remote elemental analysis using laser-induced breakdown spectroscopy (LIBS) has been developed and has been used to determine the concentration of lead in samples of dry paint. To develop a suitable fiber- optic sensor for remote measurements using LIBS a number of key issues must be addressed. The issue of coupling high-power laser pulses into optical fibers without fiber damage was first addressed by measuring damage threshold values, and by performing long-term durability tests for several different fiber types and sizes. This study led to the design of a highly flexible fiber-optic LIBS probe that can be used for a variety of sample substrates. To address the issue of reproducibility, we are investigating matrix affects and the dynamics of the laser ablation and laser-induced plasma processes by using a variety of spectroscopic techniques including time-resolved spectroscopic imaging. We have also modified the probe so that laser ablated material can be injected into a mass spectrometer.

Marquardt, Brian J.; Cullum, Brian M.; Shaw, Tim J.; Angel, S. M.

1997-05-01

186

Repopulation of nitrogen excited triplet state following laser-induced filamentation.  

PubMed

Laser-induced filamentation was used to study the dynamics of excited molecular nitrogen decay processes. It is well-known that upper excited nitrogen triplet states can be repopulated at time delays far longer than their fluorescence lifetimes. Examination of the time-resolved emission from several different species indicates that there are two major mechanisms acting to repopulate the N2(C(3)?u) excited state. The results implicate dissociative electron recombination with the nitrogen cation dimer, N4(+), and energy pooling between two N2(A(3)?u(+)) triplet states as the main pathways to repopulate the emissive upper triplet state. The densities of N2(A(3)?u(+)) and free electrons produced during filamentation were measured under atmospheric pressures in nitrogen and estimated to be [N2(A(3)?u(+))]0 = 3 × 10(15) cm(–3) and [e(–)]0 = 3 × 10(13) cm(–3). The methods outlined in this report could find significant utility in measuring the concentration profiles of these important reactive intermediates within laser-induced filaments produced under different conditions. PMID:24991979

Arnold, Bradley R; Roberson, Stephen D; Pellegrino, Paul M

2014-11-13

187

Analysis of moving surface structures at a laser-induced boiling front  

NASA Astrophysics Data System (ADS)

Recently ultra-high speed imaging enabled to observe moving wave patterns on metal melts that experience laser-induced boiling. In laser materials processing a vertical laser-induced boiling front governs processes like keyhole laser welding, laser remote fusion cutting, laser drilling or laser ablation. The observed waves originate from temperature variations that are closely related to the melt topology. For improved understanding of the essential front mechanisms and of the front topology, for the first time a deeper systematic analysis of the wave patterns was carried out. Seven geometrical shapes of bright or dark domains were distinguished and categorized, in particular bright peaks of three kinds and dark valleys, often inclined. Two categories describe special flow patterns at the top and bottom of the front. Dynamic and statistical analysis has revealed that the shapes often combine or separate from one category to another when streaming down the front. The brightness of wave peaks typically fluctuates during 20-50 ?s. This variety of thermal wave observations is interpreted with respect to the accompanying surface topology of the melt and in turn for governing local mechanisms like absorption, shadowing, boiling, ablation pressure and melt acceleration. The findings can be of importance for understanding the key process mechanisms and for optimizing laser materials processing.

Matti, R. S.; Kaplan, A. F. H.

2014-10-01

188

Analysis on laser-induced thermoelastic deformation of DMs  

NASA Astrophysics Data System (ADS)

Laser-induced static surface shape changes of deformable mirrors will cause difficulties for beam control of the laser system. The overall peak and valley (PV) value of the deformable mirror (DM) will reach the scale of micrometer when irradiated by high power lasers. We have investigated changes in the static surface shape of a 37-element DM caused by laser-induced thermoelastic deformation. It is found that the laser-induced profile change of the mirror shows a high-order characteristic. In this paper the finite element method is used to analyze the surface shape of the DM when it is irradiated by high power lasers. The surface shape is fitted using the Zernike polynomials and the influence functions to see the characteristic of it and the DM's ability to compensate it. The fitting results show that the lower-order aberrations can be corrected by the DM itself with the cost of a reduced ability of aberration correction, as the available amount of stroke will decrease. In addition, changes of the influence functions are simulated and the modified influence functions are calculated. Furthermore, the performances of the DM in three different situations are simulated to reveal the impact of thermoelastic deformation on the DM's aberration correcting ability.

Wei, Binbin; Liu, Wenguang; Xie, Kun; Jiang, Zongfu; Zhou, Qiong

2014-11-01

189

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

190

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

191

A Wide Dynamics and Fast Scan Interrogating Method for a Fiber Bragg Grating Sensor Network Implemented Using Code Division Multiple Access  

PubMed Central

We propose and demonstrate a fiber Bragg grating (FBG) sensor network employing the code division multiple access (CDMA) technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two different signals with the same pseudo-random binary sequence (PRBS) pattern, but slightly different frequencies, are applied to the source and detector sides. Moreover, for time domain detection, a wavelength-to-time conversion technique using a wavelength dispersive medium is introduced. The experimental results show that the proposed sensor network has a wide strain dynamic range of 2,400 ?? and a low crosstalk of 950:1. PMID:22778619

Kim, Youngbok; Jeon, Sie-Wook; Kwon, Won-Bae; Park, Chang-Soo

2012-01-01

192

Two-dimensional fluorescence-detected coherent spectroscopy with absolute phasing by confocal imaging of a dynamic grating and 27-step phase-cycling  

SciTech Connect

We present a novel experimental scheme for two-dimensional fluorescence-detected coherent spectroscopy (2D-FDCS) using a non-collinear beam geometry with the aid of “confocal imaging” of dynamic (population) grating and 27-step phase-cycling to extract the signal. This arrangement obviates the need for distinct experimental designs for previously developed transmission detected non-collinear two-dimensional coherent spectroscopy (2D-CS) and collinear 2D-FDCS. We also describe a novel method for absolute phasing of the 2D spectrum. We apply this method to record 2D spectra of a fluorescent dye in solution at room temperature and observe “spectral diffusion.”.

De, Arijit K., E-mail: akde@lbl.gov; Fleming, Graham R., E-mail: grfleming@lbl.gov [Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94702 (United States); Department of Chemistry, University of California at Berkeley, Berkeley, California 94702 (United States); Monahan, Daniele; Dawlaty, Jahan M. [Department of Chemistry, University of California at Berkeley, Berkeley, California 94702 (United States)

2014-05-21

193

A wide dynamics and fast scan interrogating method for a fiber Bragg grating sensor network implemented using code division multiple access.  

PubMed

We propose and demonstrate a fiber Bragg grating (FBG) sensor network employing the code division multiple access (CDMA) technique to identify information from individual sensors. To detect information without considering time delays between sensors, a sliding correlation method is applied, in which two different signals with the same pseudo-random binary sequence (PRBS) pattern, but slightly different frequencies, are applied to the source and detector sides. Moreover, for time domain detection, a wavelength-to-time conversion technique using a wavelength dispersive medium is introduced. The experimental results show that the proposed sensor network has a wide strain dynamic range of 2,400 ?? and a low crosstalk of 950:1. PMID:22778619

Kim, Youngbok; Jeon, Sie-Wook; Kwon, Won-Bae; Park, Chang-Soo

2012-01-01

194

Analysis of metallic multilayers using hypersonic surface waves induced by transient reflecting gratings  

Microsoft Academic Search

Gigahertz surface accoustic waves (the Rayleigh-like modes) have been optically generated and detected on ultrathin (less than 1 micron) metallic single-layer and multilayered films attached to glass substrates using the laser-induced transient reflecting grating (TRG) technique. The dispersion relations of the excited Rayleigh-like modes could be constructed experimentally and theoretically. By finding the best fitting of the theoretical dispersion curves

Qing Shen; Akira Harata; Tsuguo Sawada

1993-01-01

195

Optimization of laser-induced choroidal neovascularization in African green monkeys  

Microsoft Academic Search

We developed and validated a new nonhuman primate model of laser-induced choroidal neovascularization (CNV) that addresses study design limitations prevalent in laser-induced CNV-based efficacy studies. Laser-induced Bruch’s membrane disruption triggers CNV and has been widely utilized in animals to model neovascular (“wet”) age-related macular degeneration (AMD). Despite widespread use of the approach, detailed assessment of experimental parameters and their influence

Robin J. Goody; Wenzheng Hu; Afshin Shafiee; Michael Struharik; Stephen Bartels; Francisco J. López; Matthew S. Lawrence

2011-01-01

196

Time-resolved photoacoustic spectroscopy using fiber Bragg grating acoustic transducers  

Microsoft Academic Search

An acoustic transducer based on a fiber Bragg grating (FBG) is presented\\u000a and characterized for use in time-resolved laser-induced photoacoustic\\u000a spectroscopy (PAS) on solid samples. The photoacoustic wave was\\u000a generated by pulsed laser excitation of immobilized carbon black or\\u000a erbium oxide powder, and detected by recording either the transmission\\u000a or reflection spectrum of a clamped fiber Bragg grating (FBG). The

Qingxin Yang; Jack Barnes; Hans-Peter Loock; David Pedersen

2007-01-01

197

Spectral selective radio frequency emissions from laser induced breakdown of target materials  

NASA Astrophysics Data System (ADS)

The radio frequency emissions scanned over broad spectral range (30 MHz-1 GHz) from single shot nanosecond (7 ns) and picosecond (30 ps) laser induced breakdown (LIB) of different target materials (atmospheric air, aluminum, and copper) are presented. The dominant emissions from ns-LIB, compared to those from the ps-LIB, indicate the presence and importance of atomic and molecular clusters in the plasma. The dynamics of laser pulse-matter interaction and the properties of the target materials were found to play an important role in determining the plasma parameters which subsequently determine the emissions. Thus, with a particular laser and target material, the emissions were observed to be spectral selective. The radiation detection capability was observed to be relatively higher, when the polarization of the input laser and the antenna is same.

Vinoth Kumar, L.; Manikanta, E.; Leela, Ch.; Prem Kiran, P.

2014-08-01

198

Interaction and fragmentation of pulsed laser induced microbubbles in a narrow gap.  

PubMed

We investigate the interaction dynamics of an existing stable microbubble B1 and another laser induced nearby expanding microbubble B2 in a thin ink sheet between two glass slices. The fast expanding B2 causes anistropic compression of B1 with a forward penetrating jet. In the subsequent expansion stage of B1, the gas associated with jet protrusion to the opposite edge of B1 and the nonuniform surrounding flow field induce necking with transverse inward jetting from the side lobes, which further interact with the axial jet and lead to the final fragmentation into smaller bubbles. At small interbubble distance, the backward interaction from B1 first leads to the pointed pole of the expanding B2 and then a backward jetting during its collapsing. The strong interaction can merge the two bubbles with complicated asymmetric intermediated patterns. PMID:16486714

Chen, Yen-Hong; Chu, Hong-Yu; I, Lin

2006-01-27

199

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

200

Simulated characterization of soot in the flame based on laser induced incandescence  

NASA Astrophysics Data System (ADS)

The unburned carbon particle, formed due to incomplete combustion of fossil fuel, biofuel, and biomass, raises great environmental and health problems. During the measurement of flames, a non-intrusive and in situ optical method is preferred rather than probe sampling method. Also the method with high spatial resolution and high temporal resolution is required for fast dynamic reactions such as combustion research. The technique based on laser-induced incandescence (LII) has been developed to characterize the soot particles. In this work, the simulation of LII signals have been did. In the simulation, different parameters have been applied and acquired corresponding results. The method provides theoretical results to analyze LII signals, and will eventually use in experimentation

Hou, Yanping; Chen, Jun; Yang, Huinan; Cai, Xiaoshu

2014-12-01

201

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

202

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

NASA Astrophysics Data System (ADS)

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.

1990-06-01

203

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

204

Laser-induced orbital and spin excitations in ferromagnets: insights from a two-level system.  

PubMed

A recent time-resolved measurement showed that laser-induced orbital and spin excitations proceed in unison and the spin-orbit ratio is held constant during demagnetization. Here a two-level model shows that these orbital and spin excitations originate from state population and state interference effects. For an addressed state, spin and orbital dynamics are solely from the state interference, where the spin and orbital momenta oscillate with the laser frequency and match the dipole moment exactly, an unambiguous test case for the time-resolved magneto-optical Kerr effect. For an undressed state, the interference effect introduces a rapid beating in orbital momentum, which is observed in the first-principles calculation in fcc Ni. The state population change leads to a constant spin-orbit ratio, which explains the linear dependence between spin and orbital momentum changes within 2 ps upon the arrival of a pump pulse in Fe. PMID:18999859

Zhang, G P

2008-10-31

205

Laser-induced fluorescence in high pressure solid propellant flames  

SciTech Connect

The application of laser-induced fluorescence (LIF) to the study of high pressure solid propellant flames is described. The distribution of the OH and CN radicals was determined in several solid propellant flames at pressures up to 3.5 MPa. The greatest difficulty in these measurements was the separation of the desired LIF signals from the large scattering at the laser wavelength from the very optically thick propellant flames. Raman experiments using 308-nm excitation were also attempted in the propellant flames but were unsuccessful due to LIF interferences from OH and NH.

Edwards, T.; Weaver, D.P.; Campbell, D.H.

1987-09-01

206

Optimization of confocal laser induced fluorescence in a plasma  

NASA Astrophysics Data System (ADS)

Laser Induced Fluorescence (LIF) provides measurements of flow speed, temperature, and density of ions or neutrals in a plasma. Traditionally, a LIF measurement requires two ports on a plasma device; one for laser injection and one for emission collection. Proper alignment of LIF optics is time consuming and sensitive to mechanical vibration. We describe a confocal configuration for LIF that requires a single port and requires no alignment. The measurement location is scanned radially by physically moving the entire optical structure. Confocal LIF measurements are compared to traditional LIF measurements over the same radial range.

VanDervort, R.; Elliott, D.; McCarren, D.; McKee, J.; Soderholm, M.; Sears, S.; Scime, E.

2014-11-01

207

Optimization of confocal laser induced fluorescence in a plasma.  

PubMed

Laser Induced Fluorescence (LIF) provides measurements of flow speed, temperature, and density of ions or neutrals in a plasma. Traditionally, a LIF measurement requires two ports on a plasma device; one for laser injection and one for emission collection. Proper alignment of LIF optics is time consuming and sensitive to mechanical vibration. We describe a confocal configuration for LIF that requires a single port and requires no alignment. The measurement location is scanned radially by physically moving the entire optical structure. Confocal LIF measurements are compared to traditional LIF measurements over the same radial range. PMID:25430315

VanDervort, R; Elliott, D; McCarren, D; McKee, J; Soderholm, M; Sears, S; Scime, E

2014-11-01

208

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

209

Visualization of jet development in laser-induced plasmas.  

PubMed

Laser-induced plasmas in gases are known to generate gaseous jets in the postplasma gas plume. The gaseous jet typically develops toward the laser source, and the experiments presented here show, for the first time to our knowledge, that, under certain conditions, these jets can develop in the opposite direction or may not form at all. The data suggest that this is related to the ratio between the energy absorbed in the plasma and the threshold breakdown energy, effectively leading to multiple plasma initiation sites in the focal waist. PMID:23455258

Brieschenk, Stefan; O'Byrne, Sean; Kleine, Harald

2013-03-01

210

A blood analog for laser-induced photochemical anemometry.  

PubMed

A transparent viscoelastic blood analog fluid was developed for use with Laser-Induced Photochemical Anemometry. To provide solubility of the photochemical tracer, 1', 3', 3'-trimethyl-6-nitroindoline-2-benzopyran (TNSB dye, Kodak Chemicals), the analog solvent needed to be nonpolar, thus currently available aqueous blood analogs were not suitable. An analog consisting of 0.04% ethylhydroxyethylcellulose dissolved in gamma-butyrolactone produced a pseudoplastic steady shear response with low elasticity in unsteady shear, while being compatible with the photochemical tracer. PMID:9093442

Sharp, M K; Cook, J; McCarvill, W T; Lee, C S; Arieta, F; Tarbell, J M

1996-01-01

211

Medical applications of laser-induced fluorescence: pharmacokinetics of photosensitizers  

NASA Astrophysics Data System (ADS)

Laser-induced fluorescence has been used to measure tissue levels of chloroaluminum phthalocyanine tetrasulfonate versus time in order to determine its pharmacokinetics. A hamster cheek pouch carcinoma model was used in vivo. The data have been modeled using a four compartment pharmacokinetic model, yielding rate constants which describe the transport. A minimum of 13 rate constants was needed to achieve acceptable fits to the tumor and normal tissue as well as plasma data. The model gives insight into the role of binding and unbinding processes that are not otherwise evident.

Schomacker, Kevin T.; Frisoli, Joan K.; Deutsch, Thomas F.

1993-07-01

212

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

213

Laser-induced photoacoustic spectroscopy investigation of colon phantom tissue  

Microsoft Academic Search

This paper discusses laser-induced photoacoustic investigations; it concerns a non-destructive technique for the determination\\u000a of the thermal diffusivity of colon phantom tissue employing open photoacoustic cell configuration.\\u000a \\u000a \\u000a The theoretical value of thermal diffusivity is determined to be 5.65×10?4 m2?s?1 and found to be comparable with other conventional thermal-diffusivity measurement techniques such as laser flash method.\\u000a The results obtained provide the evidence

James Joseph; Krishnan Sathiyamoorthy; T. Visalatchi; V. M. Murukeshan; Lye Sun Woh

2010-01-01

214

Femtosecond laser-induced electronic plasma at metal surface  

SciTech Connect

We develop a theoretical analysis to model plasma initiation at the early stage of femtosecond laser irradiation of metal surfaces. The calculation reveals that there is a threshold intensity for the formation of a microscale electronic plasma at the laser-irradidated metal surface. As the full width at half maximum of a laser pulse increases from 15 to 200 fs, the plasma formation threshold decreases by merely about 20%. The dependence of the threshold intensity on laser pulse width can be attributed to laser-induced surface electron emission, in particular due to the effect of photoelectric effect.

Chen Zhaoyang; Mao, Samuel S. [Department of Mechanical Engineering, University of California at Berkeley, Berkeley, California 94720 (United States)

2008-08-04

215

Catwalk grate lifting tool  

DOEpatents

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

Gunter, Larry W. (615 Sandpit Rd., Leesville, SC 29070)

1992-01-01

216

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

217

Kr II laser-induced fluorescence for measuring plasma acceleration.  

PubMed

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(4)D(7/2) to the 5p(4)P(5/2)(?) 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(4)D(7/2)-5p(4)P(5/2)(?) 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. PMID:23126755

Hargus, W A; Azarnia, G M; Nakles, M R

2012-10-01

218

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

219

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

220

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

221

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

222

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

223

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

224

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

225

Concept of a Single Temperature for Highly Nonequilibrium Laser-Induced Hydrogen Desorption from a Ruthenium Surface  

NASA Astrophysics Data System (ADS)

Laser-induced condensed phase reactions are often interpreted as nonequilibrium phenomena that go beyond conventional thermodynamics. Here, we show by Langevin dynamics and for the example of femtosecond-laser desorption of hydrogen from a ruthenium surface that light adsorbates thermalize rapidly due to ultrafast energy redistribution after laser excitation. Despite the complex reaction mechanism involving hot electrons in the surface region, all desorption product properties are characterized by equilibrium distributions associated with a single, unique temperature. This represents an example of ultrahot chemistry on the subpicosecond time scale.

Füchsel, G.; Tremblay, J. C.; Klamroth, T.; Saalfrank, P.; Frischkorn, C.

2012-08-01

226

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

227

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

228

Laser-Induced Fluorescence in Gaseous [I[subscript]2] Excited with a Green Laser Pointer  

ERIC Educational Resources Information Center

A green laser pointer could be used in a flashy demonstration of laser-induced fluorescence in the gas phase by directing the beam of the laser through a cell containing [I[subscript]2] at its room temperature vapor pressure. The experiment could be used to provide valuable insight into the requirements for laser-induced fluorescence (LIF) and the…

Tellinghuisen, Joel

2007-01-01

229

Barium Ion Extraction and Identification from Laser Induced Fluorescence in Gas for the  

E-print Network

Barium Ion Extraction and Identification from Laser Induced Fluorescence in Gas for the Enriched the barium ion daughter from the double beta decay of xenon-136 using laser induced fluorescence. The technique is very complex and requires an excellent understanding of the barium ion spectroscopy and its

Wechsler, Risa H.

230

Laser-induced forward transfer on compliant receivers M. Feinaeugle1  

E-print Network

Laser-induced forward transfer on compliant receivers M. Feinaeugle1 , P. Horak1 , C.L. Sones1 , R17 1BJ, UK Laser-induced forward transfer (LIFT) is a technique for the transfer of materials of a laser pulse at the interface of donor and carrier, accelerating a part of the thin film (flyer) towards

231

Thermoelectric generator fabricated via laser-induced forward transfer M.Feinaeugle1  

E-print Network

Thermoelectric generator fabricated via laser-induced forward transfer M.Feinaeugle1 , C.L. Sones1 of a thermoelectric generator with the rapid, lithography-less technique of laser-induced forward transfer (LIFT), performed under ambient conditions. LIFT is a laser-assisted method for the transfer of materials

232

Temporal and spatial evolution of C2 in laser induced plasma from graphite target  

E-print Network

Temporal and spatial evolution of C2 in laser induced plasma from graphite target S. S. Harilal February 1996; accepted for publication 10 June 1996 Laser ablation of graphite has been carried out using species in the laser induced plasma from graphite. © 1996 American Institute of Physics. S0021-8979 96

Harilal, S. S.

233

Investigation of the local structure variance of water molecules in laser-induced thermal desorption process  

NASA Astrophysics Data System (ADS)

This paper presents the use of molecular dynamics simulation in the study of laser-induced thermal desorption (LITD) of water molecules adjacent to a laser-heated Au substrate. The local structure of the water molecules is investigated by considering the densities of the oxygen and hydrogen atoms, the average number of neighbors, nNN, and the average number of H-bonds, nHB. At an equilibrium temperature of 300 K, the simulation results show that three adsorption water layers are formed in the immediate vicinity of the Au surface, and that each four-fold hollow site on the uppermost Au(0 0 1) surface is occupied by a single water molecule. Following laser-induced heating of the Au substrate with a sub-picosecond laser pulse of 350 fs, the substrate temperature increases to 1000 K. This causes a gradual heating of the adjacent water film, which is accompanied by a decrease in the values of nNN and nHB. Hence, it can be concluded that an increase in the water film temperature destroys the hydrogen-bonding network throughout the water film. Although the maximum local temperature of the water film occurs in the region immediately adjacent to the Au substrate, it is determined that the attractive energy between the Au atoms and the water molecules in this region causes the water molecules to aggregate together to form three-dimensional water clusters. Furthermore, this energy prevents the hydrogen bonds in this region from breaking apart as violently as those within the phase explosion region. Finally, it is observed that the phase explosion phenomenon occurs in the region of the water film where the values of nNN and nHB are at a minimum.

Ju, Shin-Pon; Weng, Cheng-I.

2004-05-01

234

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

235

TGCat, The Chandra Transmission Grating Catalog and Archive: Systems, Desgin and Accessibility  

E-print Network

The recently released Chandra Transmission Grating Catalog and Archive, TGCat, presents a fully dynamic on-line catalog allowing users to browse and categorize Chandra gratings observations quickly and easily, generate ...

Mitschang, Arik W.

236

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

237

Preliminary evaluation of laser induced breakdown spectroscopy for slurry samples  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) was applied to the analysis of simulant slurry samples used in the vitrification process of liquid radioactive wastes. A spectroscopic analysis was performed by two different detection systems: Czerny-Turner spectrometer coupled with intensified diode array detector (IDAD) and an Echelle spectrometer with intensified charge coupled device (ICCD). For the Czerny-Turner detection system, the normalized intensity method, which is the normalization of the atomic emission intensity by the released whole plasma emission area intensity, was employed to improve the reproducibility of LIBS signals. The Echelle detection system showed a high efficiency in simultaneous multi-element detection and determination of the physical quantities of the simulant.

Oh, Seong Yong; Yueh, Fang Yu; Singh, Jagdish P.; Herman, Connie C.; Zeigler, Kristine

2009-01-01

238

Printing biological solutions through laser-induced forward transfer  

NASA Astrophysics Data System (ADS)

Laser-induced forward transfer (LIFT) is a direct-writing technique adequate for the high-resolution printing of a wide range of materials, including biological molecules. In this article, the preparation through LIFT of microarrays of droplets from a solution containing rabbit antibody immunoglobulin G (IgG) is presented. The microarrays were prepared at different laser pulse energy conditions, obtaining microdroplets with a circular and well-defined contour. The transfer process has a double threshold: a minimum energy density required to generate an impulsion on the liquid film, and a minimum pulse energy, which corresponds to the onset for material ejection. In addition, it was demonstrated that the transfer process can be correctly described through a simple model which relates the energy density threshold with the amount of released material. Finally, a fluorescence assay was carried out in which the preservation of the activity of the transferred biomolecules was demonstrated.

Duocastella, M.; Fernández-Pradas, J. M.; Domínguez, J.; Serra, P.; Morenza, J. L.

2008-12-01

239

Laser-induced modification of transparent crystals and glasses  

SciTech Connect

We analyse the processes taking place in transparent crystals and glasses irradiated by ultrashort laser pulses in the regimes typical of various applications in optoelectronics and photonics. We consider some phenomena, which have been previously described by the authors within the different model representations: charging of the dielectric surface due to electron photoemission resulting in a Coulomb explosion; crater shaping by using an adaptive control of the laser pulse shape; optimisation of the waveguide writing in materials strongly resistant to laser-induced compaction under ordinary irradiation conditions. The developed models and analysis of the processes relying on these models include the elements of the solid-state physics, plasma physics, thermodynamics, theory of elasticity and plasticity. Some important experimental observations which require explanations and adequate description are summarised. (photonics and nanotechnology)

Bulgakova, N M [S S Kutateladze Institute of Thermophysics, Siberian Branch, Russian Academy of Sciences, Novosibirsk (Russian Federation); Stoian, Razvan [Laboratoire Hubert Curien, UMR 5516 CNRS, Universite Jean Monnet, 42000 Saint Etienne, Universite de Lyon, 42023 Saint Etienne (France); Rosenfeld, A [Max-Born-Institut fur Nichtlineare Optik und Kurzzeitspektroskopie, Berlin (Germany)

2010-12-29

240

Excimer laser induced surface nitriding of aluminium alloy  

NASA Astrophysics Data System (ADS)

This study describes a technique for the growth of thin nitride layer on aluminium alloy samples by direct laser synthesis with the advantages of good adhesion and localisation. The laser irradiation process is performed using an XeCl excimer laser ( ?=308 nm, 50 Hz) under a nitrogen atmosphere. The laser induced plasma interacts with the melted sample surface resulting in nitrogen atom diffusion and reaction into the depth of the sample. Plasma spots were overlapped by two dimensional laser beam displacement to ensure the complete coating of the surface with a specified laser fluence (1.6 J/cm 2) and number of pulses (500), while not removing of the nitride layer already synthesised. Under these conditions, the diffusion layer penetrates a few ?m deep, but its crystalline quality is preserved. Interesting information on the layer formation and composition are drawn from nuclear analysis (RBS and NRA) to determine the nitrogen and oxygen (contaminant) concentration profiles.

Sicard, E.; Boulmer-Leborgne, C.; Sauvage, T.

1998-05-01

241

Laser-induced breakdown spectroscopy analysis of energetic materials.  

PubMed

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. PMID:14594077

De Lucia, Frank C; Harmon, Russell S; McNesby, Kevin L; Winkel, Raymond J; Miziolek, Andrzej W

2003-10-20

242

Diagnostics of laser-induced plasma by optical emission spectroscopy  

NASA Astrophysics Data System (ADS)

The procedure for diagnostics of laser induced plasma (LIP) by optical emission spectroscopy technique is described. LIP was generated by focusing Nd:YAG laser radiation (1.064 nm, 50 mJ, 15 ns pulse duration) on the surface of pellet containing among other elements lithium. Details of the experimental setup and experimental data processing are presented. High speed plasma photography was used to study plasma evolution and decay. From those images optimum time for plasma diagnostics is located. The electron number density, Ne, is determined by fitting profiles of Li I lines while electron temperature, Te, was determined from relative intensities of Li I lines using Boltzmann plot (BP) technique. All spectral line recordings were tested for the presence of self-absorption and then if optically thin, Abel inverted and used for plasma diagnostic purposes.

Cveji?, M.

2014-12-01

243

Laser-induced breakdown spectroscopy (LIBS): a new spectrochemical technique  

SciTech Connect

We have used the breakdown spark from a focused laser beam to generate analytically useful emission spectra of minor constituents in air and other carrier gases. The medium was sampled directly. It was not necessary to reduce the sample to solution nor to introduce electrodes. The apparatus is particularly simple; a pulsed laser, spectrometer, and some method for time resolution. The latter is essential in laser-induced-breakdown spectroscopy (LIBS) because of the strong early continuum. High temperatures in the spark result in vaporization of small particles, dissociation of molecules, and excitation of atomic and ionic spectra, including species which are normally difficult to detect. In one application, we have monitored beryllium in air at conventrations below 1 ..mu..g/m/sup 3/, which is below 1 ppB (w/w). In another we have monitored chlorine and fluorine atoms in real time. LIBS has the potential for real-time direct sampling of contaminants in situ.

Radziemski, L.J.; Loree, T.R.; Cremers, D.A.

1982-01-01

244

Pulsed laser-induced formation of silica nanogrids  

NASA Astrophysics Data System (ADS)

Silica grids with micron to sub-micron mesh sizes and wire diameters of 50 nm are fabricated on fused silica substrates. They are formed by single-pulse structured excimer laser irradiation of a UV-absorbing silicon suboxide (SiO x ) coating through the transparent substrate. A polydimethylsiloxane (PDMS) superstrate (cover layer) coated on top of the SiO x film prior to laser exposure serves as confinement for controlled laser-induced structure formation. At sufficiently high laser fluence, this process leads to grids consisting of a periodic loop network connected to the substrate at regular positions. By an additional high-temperature annealing, the residual SiO x is oxidized, and a pure SiO2 grid is obtained.

Ihlemann, Jürgen; Weichenhain-Schriever, Ruth

2014-03-01

245

Pulsed laser-induced formation of silica nanogrids  

PubMed Central

Silica grids with micron to sub-micron mesh sizes and wire diameters of 50 nm are fabricated on fused silica substrates. They are formed by single-pulse structured excimer laser irradiation of a UV-absorbing silicon suboxide (SiO x ) coating through the transparent substrate. A polydimethylsiloxane (PDMS) superstrate (cover layer) coated on top of the SiO x film prior to laser exposure serves as confinement for controlled laser-induced structure formation. At sufficiently high laser fluence, this process leads to grids consisting of a periodic loop network connected to the substrate at regular positions. By an additional high-temperature annealing, the residual SiO x is oxidized, and a pure SiO2 grid is obtained. PACS 81.07.-b; 81.07.Gf; 81.65.Cf PMID:24581305

2014-01-01

246

Apparatus, system, and method for laser-induced breakdown spectroscopy  

DOEpatents

In laser-induced breakdown spectroscopy (LIBS), an apparatus includes a pulsed laser configured to generate a pulsed laser signal toward a sample, a constructive interference object and an optical element, each located in a path of light from the sample. The constructive interference object is configured to generate constructive interference patterns of the light. The optical element is configured to disperse the light. A LIBS system includes a first and a second optical element, and a data acquisition module. The data acquisition module is configured to determine an isotope measurement based, at least in part, on light received by an image sensor from the first and second optical elements. A method for performing LIBS includes generating a pulsed laser on a sample to generate light from a plasma, generating constructive interference patterns of the light, and dispersing the light into a plurality of wavelengths.

Effenberger, Jr., Andrew J; Scott, Jill R; McJunkin, Timothy R

2014-11-18

247

Laser-induced stress transients: applications for molecular delivery  

NASA Astrophysics Data System (ADS)

Lasers can be used to enhance the delivery of a number of molecules. Other investigators have demonstrated local release of molecules from liposomes following laser irradiation, microbeam disruption of the cell membrane to increase cell transport, microbeam ablation of the zona pellucida surrounding the ovum to increase the chances of fertilization, and increased transcutaneous transport following ablation of the stratum corneum. Our experiments have shown that laser-induced stress transients can be utilized as a vector for intracellular delivery of molecules that may or may not normally cross the cell membrane. These two conditions have been tested with Photofrin and DNA. This technology may have applications in cell and molecular biology, cancer therapy, gene therapy, and others.

Flotte, Thomas J.; Lee, Shun; Zhang, Hong; McAuliffe, Daniel J.; Douki, Tina; Doukas, Apostolos G.

1995-05-01

248

Adaptive femtosecond laser-induced breakdown spectroscopy of uranium.  

PubMed

Laser-induced breakdown spectroscopy (LIBS) is an established technique for material characterization applicable to a variety of problems in research, industry, environmental studies, and security. LIBS conducted with femtosecond laser pulses exhibits unique properties, arising from the characteristics of laser-matter interactions in this pulse width regime. The time evolution of the electric field of the pulse determines its interaction with sample materials. We present the design and performance of a femtosecond LIBS system developed to systematically optimize the technique for detection of uranium. Sample analysis can be performed in vacuum environment, and the spectral and temporal diagnostics are coupled through an adaptive feedback loop, which facilitates optimization of the signal-to-noise ratio by pulse shaping. Initial experimental results of LIBS on natural uranium are presented. PMID:23387634

Ko, P; Hartig, K C; McNutt, J P; Schur, R B D; Jacomb-Hood, T W; Jovanovic, I

2013-01-01

249

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

250

Prediction of absorption coefficients by pulsed laser induced photoacoustic measurements.  

PubMed

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 281nm 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 0.035mM. The photoacoustic experiments were also performed with various tryptophan concentrations at 281nm 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. PMID:24632160

Priya, Mallika; Satish Rao, B S; Ray, Satadru; Mahato, K K

2014-06-01

251

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

252

OH Planar Laser-Induced Fluorescence from Microgravity Droplet Combustion  

NASA Technical Reports Server (NTRS)

Droplet combustion under microgravity conditions has been extensively studied, but laser diagnostics have just begun to be employed in microgravity droplet experiments. This is due in part to the level of difficulty associated with laser system size, power and economic availability. Hydroxyl radical (OH) is an important product of combustion, and laser-induced fluorescence (LIF) has proved to be an adequate and sensitive tool to measure OH. In this study, a frequency doubled Nd:YAG laser and a doubled dye laser, compact and reliable enough to perform OH PLIF experiments aboard a parabolic flight-path aircraft, has been developed and successfully demonstrated in a methanol droplet flame experiment. Application to microgravity conditions is planned aboard parabolic flight-path aircraft.

Winter, Michael; Wegge, Jason; Kang, Kyung-Tae

1997-01-01

253

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

254

Laser-induced atomic adsorption: A mechanism for nanofilm formation  

NASA Astrophysics Data System (ADS)

We demonstrate and interpret a technique of laser-induced formation of thin metallic films using alkali atoms on the window of a dense-vapour cell. We show that this intriguing photo-stimulated process originates from the adsorption of Cs atoms via the neutralization of Cs+ ions by substrate electrons. The Cs+ ions are produced via two-photon absorption by excited Cs atoms very close to the surface, which enables the transfer of the laser spatial intensity profile to the film thickness. An initial decrease of the surface work function is required to guarantee Cs+ neutralization and results in a threshold in the vapour density. This understanding of the film growth mechanism may facilitate the development of new techniques of laser-controlled lithography, starting from thermal vapours.

Martins, Weliton S.; Passerat de Silans, Thierry; Oriá, Marcos; Chevrollier, Martine

2013-11-01

255

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

256

Laser-induced vibration of a thin soap film.  

PubMed

We report on the vibration of a thin soap film based on the optical radiation pressure force. The modulated low power laser induces a counter gravity flow in a vertical free-standing draining film. The thickness of the soap film is then higher in the upper region than in the lower region of the film. Moreover, the lifetime of the film is dramatically increased by a factor of 2. Since the laser beam only acts mechanically on the film interfaces, such a film can be employed in an optofluidic diaphragm pump, the interfaces behaving like a vibrating membrane and the liquid in-between being the fluid to be pumped. Such a pump could then be used in delicate micro-equipment, in chips where temperature variations are detrimental and even in biological systems. PMID:25017934

Emile, Olivier; Emile, Janine

2014-09-21

257

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

258

Picosecond electron deflectometry of laser-induced plasmas  

NASA Astrophysics Data System (ADS)

We demonstrate a method for real-time imaging of the field distribution in laser-induced plasmas with picosecond temporal resolution. The plasma is generated by a 50 fs laser pulse focused in nitrogen gas jet, and is then probed by a picosecond electron pulse synchronized with the laser. Pump-probe images of the electron beam at different delay times are recorded on a CCD camera. The electric and magnetic fields are reconstructed by comparing the recorded patterns with numerical simulations. We have observed a cloud of hot electrons expanding away from a central core of positively charged ions, and the appearance of strong magnetic fields near the boundaries of the gas jet. In the case of a plasma generated in low density nitrogen (10^13 cm-3), we observed that even low energy electrons can escape from the plasma volume.

Centurion, Martin; Reckenthaeler, Peter; Apolonskiy, Alexander; Krausz, Ferenc; Fill, Ernst

2008-11-01

259

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

260

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

261

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

262

Advancements in time-resolved x-ray laser induced time-of-flight photoelectron spectroscopy  

NASA Astrophysics Data System (ADS)

Time-resolved soft x-ray photoelectron spectroscopy is used to probe the non-steady-state evolution of the valence band electronic structure of laser heated ultra-thin (50 nm) metal foils and bulk semiconductors. Single-shot soft x-ray laser induced time-of-flight photoelectron spectroscopy with picosecond time resolution was used in combination with optical measurements of the disassembly dynamics that have shown the existence of a metastable liquid phase in fs-laser heated metal foils persisting 4-5 ps. This metastable phase is studied using a 527 nm wavelength 400 fs laser pulse containing 0.3 - 2.5 mJ laser energy focused in a large 500 × 700 ?m2 spot to create heated conditions of 0.2 - 1.8 × 1012 W cm-2 intensity. The unique LLNL COMET compact tabletop soft x-ray laser source provided the necessary high photon flux, highly monoenergetic, picosecond pulse duration, and coherence for observing the evolution of changes in the valence band electronic structure of laser heated metals and semiconductors with picosecond time resolution. This work demonstrates the continuing development of a powerful new technique for probing reaction dynamics and changes of local order on surfaces on their fundamental timescales including phenomena such as non-thermal melting, chemical bond formation, intermediate reaction steps, and the existence of transient reaction products.

Nelson, A. J.; Dunn, J.; Widmann, K.; Ao, T.; Ping, Y.; Hunter, J.; Ng, A.

2005-09-01

263

Laser-induced incandescence measurements in a fired diesel engine at 3 kHz  

NASA Astrophysics Data System (ADS)

Laser-induced incandescence (LII) was performed at 3 kHz in an optically accessible cylinder of a fired diesel engine using a commercially available diode-pumped solid-state laser and an intensified CMOS camera. The resulting images, acquired every 3° of crank angle, enabled the spatiotemporal tracking of soot structures during the expansion/exhaust stroke of the engine cycle. The image sequences demonstrate that soot tends to form in thin sheets that propagate and interact with the in-cylinder flow. These sheets tend to align parallel to the central axis of the cylinder and are frequently wrapped into conical spirals by aerodynamic swirl. Most of the soot is observed well away from the cylinder walls. Quantitative soot measurements were beyond the scope of this study but the results demonstrate the practical utility of using kHz-rate LII to acquire ensemble-averaged statistical data with high crank angle resolution over a complete engine cycle. Based on semi-quantitative measures of soot distribution, it was possible to identify soot dynamics related to incomplete charge exchange. This study shows that long-duration, multi-kHz acquisition rate LII measurements are viable in a fired diesel engine with currently available laser and camera technology, albeit only in the expansion and exhaust phase of the cycle at present. Furthermore, such measurements yield useful insight into soot dynamics and therefore constitute an important new tool for the development and optimization of diesel engine technology.

Boxx, I. G.; Heinold, O.; Geigle, K. P.

2015-01-01

264

Modeling of laser-induced plume expansion into ambient gas for thin film deposition  

NASA Astrophysics Data System (ADS)

The expansion of laser-induced plume into an ambient gas under typical thin film deposition conditions is investigated. A simplified theoretical model has been developed to understand the dynamics of plume-ambient gas interaction under the gas pressure of typically a few tens Pa. The model is based upon the generation of a high-temperature and high-pressure plasma cloud which is initially confined to a sphere of irradiated spot radius and is then suddenly allowed to expand into a gas. The expansion is governed by the Euler system of nonstationary equations. The model has been applied to investigate the dynamics of laser ablation of YBaCuO in oxygen. Numerical results show that the series of density jumps following one after another are formed in the plume. The origin of these pulsations is attributed to the repeated reflections of the secondary shock wave due to the effect of plume overexpansion. Using the calculated data, the time-of-flight signal has been simulated to compare the numerical results with available experimental data. Surprisingly good quantitative agreement has been achieved.

Bulgakova, Nadezhda M.; Bulgakov, Alexander V.

1995-04-01

265

Laser induced molecular motion in strong nonresonant laser fields  

NASA Astrophysics Data System (ADS)

The optical dipole force from a singe focussed laser beam was used to study the role of laser-induced molecular alignment on the centre-of-mass motion of carbon disulphide molecules in a molecular beam. The translational, rotational and vibrational temperatures of the carbon disulphide molecules were measured to be 3.4pm0.2 K, 35pm10 K and 250pm14 K respectively. The velocity of the beam was measured to be 542pm22 m s. {-1}. Time-of-flight mass spectroscopy was used to measure the acceleration and deceleration of the molecules. Maximum velocity changes of 7.5 m s. {-1} and 10 m s. {-1} were recorded for linearly and circularly polarised light respectively. These results showed that the dipole force, digamma alpha bigtriangledown [alpha_e_f_f(I)I(r)], where alpha_e_f_f is the effective polarisability and determined through laser-induced alignment, can be modified by changing the laser polarisation. For linearly and circularly polarised light, a 12% difference in effective polarisability was measured to produce a 20% difference in dipole force. The dipole force from a single focussed laser beam produces a molecular optical lens and the downstream density of the molecular focus was probed by measuring the ion signal for both laser polarisations. The focal lengths for linearly and circularly polarised light were found to be separated by 100 mu m. By altering the laser polarisation from linearly through elliptically to circularly polarised light, the focal length of the molecular optical lens could be smoothly altered over the 100 mu m focal range. The role of the effective polarisability of each rotational state was also studied numerically. Separate rotational states were found to significantly alter the focal properties of a molecular optical lens. In carbon disulphide, higher rotational states (J > 10), exhibit less molecular alignment and when occupied, the focal length of the molecular optical lens for these states was increased by 60 % compared to the ground state.

Purcell, S. M.

266

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

267

APPLICATIONS OF CAPILLARY ELECTROPHORESIS/LASER-INDUCED FLUORESCENCE DETECTION TO GROUND WATER MIGRATION STUDIES  

EPA Science Inventory

Capillary electrophoresis (CE) has been applied to the determination of groundwater migration based on laser-induced fluorescence (LIF) detection and traditional spectrofluorimetry. The detection limits of injected dye-fluorescent whitening agent (tinopal) in the low parts per tr...

268

CAPILLARY ELECTROPHORESIS/LASER-INDUCED FLUORESCENCE DETECTION OF FLUORESCEIN AS A GROUNDWATER MIGRATION TRACER  

EPA Science Inventory

Capillary electrophoresis (CE) has been applied to the determination of the groundwater migration tracer dye fluorescein based on laser-induced fluorescence (LIF) detection and compared to determinations obtained with traditional spectrofluorimetry. Detection limits of injected d...

269

Spectroscopic characterization of laser-induced tin plasma S. S. Harilal,a  

E-print Network

Spectroscopic characterization of laser-induced tin plasma S. S. Harilal,a Beau O'Shay, and Mark. S 2005 Optical emission spectroscopic studies have been carried out on a tin plasma generated using 1064

Harilal, S. S.

270

Ultrafast Laser Induced Thermo-Elasto-Visco-Plastodynamics in Single Crystalline Silicon  

E-print Network

pulse width in Laser Induced Stress Waves Thermometry (LISWT) for single crystalline silicon processing motivated the work. The model formulation developed is of a hyperbolic type capable of characterizing non-thermal melting and thermo...

Qi, Xuele

2011-02-22

271

Laser-Induced Fluorescence in plasmas at UC Irvine  

NASA Astrophysics Data System (ADS)

For about 25 years laser-induced fluorescence (LIF) has been performed at UC Irvine with many people contributing over that time period. A central contributor to the work has been Raul Stern, whether directly involved with the experiments at hand or via physics advice obtained wherever he could be found worldwide spreading the joys of LIF. At Irvine LIF has been developed (1,2) and used for ion tagging (3), spatial diffusion (4,5), velocity-space diffusion (6), optical tomography (7), and plasma processing (8) among many other fascinating experimental results. This talk will review the LIF work at Irvine with special note of Stern's contributions and influence. 1.) D. Hill, S. Fornaca, M. Wickham, Rev. Sci. Instrum. 54, 309 (1983) 2.) G.D. Severn, D.A. Edrich, and R. McWilliams, Rev. Sci. Instrum. 69, 10 (1998). 3.) R. Stern, D. Hill, N. Rynn, Phys. Lett. A93, 127 (1983) 4.) M. Okubo, R. McWilliams, Phys. Fluids 30, 2849 (1987). 5.) R. McWilliams, M. K. Okubo and N. S. Wolf, Phys. Fluids B 2(3), 523 (1990). 6.) J. Bowles, R. McWilliams, N. Rynn, Phys. Plasmas 1, 3814 (1994). 7.) R. McWilliams, R. Koslover), Phys. Rev. Lett. 58, 37 (1987). 8.) R. McWilliams, D. Edrich, Thin Solid Films 435, 1 (2003).

McWilliams, R.

2003-10-01

272

Laser-induced porous graphene films from commercial polymers  

NASA Astrophysics Data System (ADS)

The cost effective synthesis and patterning of carbon nanomaterials is a challenge in electronic and energy storage devices. Here we report a one-step, scalable approach for producing and patterning porous graphene films with three-dimensional networks from commercial polymer films using a CO2 infrared laser. The sp3-carbon atoms are photothermally converted to sp2-carbon atoms by pulsed laser irradiation. The resulting laser-induced graphene (LIG) exhibits high electrical conductivity. The LIG can be readily patterned to interdigitated electrodes for in-plane microsupercapacitors with specific capacitances of >4?mF?cm?2 and power densities of ~9?mW?cm?2. Theoretical calculations partially suggest that enhanced capacitance may result from LIG’s unusual ultra-polycrystalline lattice of pentagon-heptagon structures. Combined with the advantage of one-step processing of LIG in air from commercial polymer sheets, which would allow the employment of a roll-to-roll manufacturing process, this technique provides a rapid route to polymer-written electronic and energy storage devices.

Lin, Jian; Peng, Zhiwei; Liu, Yuanyue; Ruiz-Zepeda, Francisco; Ye, Ruquan; Samuel, Errol L. G.; Yacaman, Miguel Jose; Yakobson, Boris I.; Tour, James M.

2014-12-01

273

Kalman Filtered MR Temperature Imaging for Laser Induced Thermal Therapies  

PubMed Central

The feasibility of using a stochastic form of Pennes bioheat model within a 3D finite element based Kalman filter (KF) algorithm is critically evaluated for the ability to provide temperature field estimates in the event of magnetic resonance temperature imaging (MRTI) data loss during laser induced thermal therapy (LITT). The ability to recover missing MRTI data was analyzed by systematically removing spatiotemporal information from a clinical MR-guided LITT procedure in human brain and comparing predictions in these regions to the original measurements. Performance was quantitatively evaluated in terms of a dimensionless L2 (RMS) norm of the temperature error weighted by acquisition uncertainty. During periods of no data corruption, observed error histories demonstrate that the Kalman algorithm does not alter the high quality temperature measurement provided by MR thermal imaging. The KF-MRTI implementation considered is seen to predict the bioheat transfer with RMS error < 4 for a short period of time, ?t < 10sec, until the data corruption subsides. In its present form, the KF-MRTI method currently fails to compensate for consecutive for consecutive time periods of data loss ?t > 10sec. PMID:22203706

Fuentes, D.; Yung, J.; Hazle, J. D.; Weinberg, J. S.; Stafford, R. J.

2013-01-01

274

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

275

Independent component analysis classification of laser induced breakdown spectroscopy spectra  

NASA Astrophysics Data System (ADS)

The ChemCam instrument on board Mars Science Laboratory (MSL) rover uses the laser-induced breakdown spectroscopy (LIBS) technique to remotely analyze Martian rocks. It retrieves spectra up to a distance of seven meters to quantify and to quantitatively analyze the sampled rocks. Like any field application, on-site measurements by LIBS are altered by diverse matrix effects which induce signal variations that are specific to the nature of the sample. Qualitative aspects remain to be studied, particularly LIBS sample identification to determine which samples are of interest for further analysis by ChemCam and other rover instruments. This can be performed with the help of different chemometric methods that model the spectra variance in order to identify a the rock from its spectrum. In this paper we test independent components analysis (ICA) rock classification by remote LIBS. We show that using measures of distance in ICA space, namely the Manhattan and the Mahalanobis distance, we can efficiently classify spectra of an unknown rock. The Mahalanobis distance gives overall better performances and is easier to manage than the Manhattan distance for which the determination of the cut-off distance is not easy. However these two techniques are complementary and their analytical performances will improve with time during MSL operations as the quantity of available Martian spectra will grow. The analysis accuracy and performances will benefit from a combination of the two approaches.

Forni, Olivier; Maurice, Sylvestre; Gasnault, Olivier; Wiens, Roger C.; Cousin, Agnès; Clegg, Samuel M.; Sirven, Jean-Baptiste; Lasue, Jérémie

2013-08-01

276

Laser-induced deformation on hard disk surface  

NASA Astrophysics Data System (ADS)

Laser-induced deformation on hard disk surface has been studied. A diode-pumped Q-switched Nd:YVO 4 laser was used in the experiment. The sample is a commercial hard disk. Atomic force microscope (AFM) was employed to analyze the surface morphology after laser irradiation. Depending on the laser fluence used, a radial structure with or without a circular protruding center could be obtained. Auger electron spectroscopy (AES) analyses on different sputtered level were performed to analyze the compositions at irradiated and unirradiated areas. The mechanisms of surface deformation are proposed qualitatively based on the results. Since the upper three layers, the carbon, magnetic and chromium layers, are quite thin and have higher melting points than that of the underlying nickel-phosphorous layer, the radial structure is possibly due to the interfacial stress developed during the localized sub-surface melting of the nickel-phosphorous layer. The circular protruding center is probably resulted by the whole surface melting due to higher local laser fluence.

Liu, D. M.; Lu, Y. F.; Yuan, Y.; Wang, W. J.; Low, T. S.; Wee, T. S.; Chang, K. T.; Goh, J. K.

1999-01-01

277

Elemental analysis of fertilizer using laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

In recent years, the use of fertilizers has increased to achieve high growth rate of agriculture products. With this increase the chemical impact of agricultural activities on the environment has also been enhanced. In order to keep the environment healthy, and clean, it is necessary to identify contaminants and characterize the sources of contamination. In this study, a comprehensive chemical characterization of a DAP fertilizer has been carried out using laser induced breakdown spectroscopy. Phosphorous, manganese, magnesium, iron, titanium, molybdenum, nickel, cobalt, aluminum, chromium, lead, and uranium traces are detected. Relative abundances of Phosphorous, manganese, magnesium, molybdenum, iron, titanium, nickel, vanadium, calcium, cobalt, cadmium, tin are 26.64, 17.75, 13 97, 8.25, 7.97, 7.11, 5.07, 3.15, 2.94, 1.94, 1,55, 1.73 percent, respectively, whereas relative abundances of sulfur, aluminum, chromium, lead, and uranium are less than 1% and their sum is 1.93% of the total sample.

Farooq, W. A.; Al-Mutairi, F. N.; Khater, A. E. M.; Al-Dwayyan, A. S.; AlSalhi, M. S.; Atif, M.

2012-06-01

278

Planar laser-induced fluorescence imaging in shock tube flows  

NASA Astrophysics Data System (ADS)

The planar laser-induced fluorescence (PLIF) imaging method was used to perform flow visualization and quantitative planar thermometry in shock tube flow fields using toluene as a fluorescence tracer in nitrogen. Fluorescence quantum yield values needed to quantify PLIF images were measured in a static cell at low pressures (<1 bar) for various toluene partial pressures in nitrogen bath gas. Images behind incident and reflected shocks were taken in the core flow away from regions affected by boundary layers. Temperature measurements from these images were successfully compared with predicted values using ideal shock equations. Measured temperatures ranged between 296 and 800 K and pressures between 0.15 and 1.5 atm. The average temperature discrepancies between measurements and the predicted values behind the incident and reflected shocks were 1.6 and 3.6%, respectively. Statistical analyses were also conducted to calculate the temperature measurement uncertainty as a function of image resolution. The technique was also applied to the study of more complex supersonic flows, specifically the interaction of a moving shock with a wedge. Measured temperatures agreed well with the results of numerical simulations in all inviscid regions, and all pertinent features of the single Mach reflection were resolved.

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

2010-10-01

279

Infrared laser induced plasma diagnostics of silver target  

NASA Astrophysics Data System (ADS)

In the present work, the optical emission spectra of silver (Ag) plasma have been recorded and analyzed using the laser induced breakdown spectroscopy technique. The emission line intensities and plasma parameters were investigated as a function of lens to sample distance, laser irradiance, and distance from the target surface. The electron number density (ne) and electron temperature (Te) were determined using the Stark broadened line profile and Boltzmann plot method, respectively. A gradual increase in the spectral line intensities and the plasma parameters, ne from 2.89 × 1017 to 3.92 × 1017 cm-3 and Te from 4662 to 8967 K, was observed as the laser irradiance was increased 2.29 × 1010-1.06 × 1011 W cm-2. The spatial variations in ne and Te were investigated from 0 to 5.25 mm from the target surface, yielding the electron number density from 4.78 × 1017 to 1.72 × 1017 cm-3 and electron temperature as 9869-3789 K. In addition, the emission intensities and the plasma parameters of silver were investigated by varying the ambient pressure from 0.36 to 1000 mbars.

Ahmat, L.; Ahmed, I.; Nadeem, Ali

2014-09-01

280

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

281

Laser-induced porous graphene films from commercial polymers.  

PubMed

The cost effective synthesis and patterning of carbon nanomaterials is a challenge in electronic and energy storage devices. Here we report a one-step, scalable approach for producing and patterning porous graphene films with three-dimensional networks from commercial polymer films using a CO2 infrared laser. The sp(3)-carbon atoms are photothermally converted to sp(2)-carbon atoms by pulsed laser irradiation. The resulting laser-induced graphene (LIG) exhibits high electrical conductivity. The LIG can be readily patterned to interdigitated electrodes for in-plane microsupercapacitors with specific capacitances of >4?mF?cm(-2) and power densities of ~9?mW?cm(-2). Theoretical calculations partially suggest that enhanced capacitance may result from LIG's unusual ultra-polycrystalline lattice of pentagon-heptagon structures. Combined with the advantage of one-step processing of LIG in air from commercial polymer sheets, which would allow the employment of a roll-to-roll manufacturing process, this technique provides a rapid route to polymer-written electronic and energy storage devices. PMID:25493446

Lin, Jian; Peng, Zhiwei; Liu, Yuanyue; Ruiz-Zepeda, Francisco; Ye, Ruquan; Samuel, Errol L G; Yacaman, Miguel Jose; Yakobson, Boris I; Tour, James M

2014-01-01

282

Laser induced damage and fracture in fused silica vacuum windows  

SciTech Connect

Laser-induced damage, that initiates catastrophic fracture, has been observed in large ({le}61 cm dia) fused silica lenses that also serve as vacuum barriers in Nova and Beamlet lasers. If the elastic stored energy in the lens is high enough, the lens will fracture into many pieces (implosion). Three parameters control the degree of fracture in the vacuum barrier window: elastic stored energy (tensile stress), ratio of window thickness to flaw depth, and secondary crack propagation. Fracture experiments were conducted on 15-cm dia fused silica windows that contain surface flaws caused by laser damage. Results, combined with window failure data on Beamlet and Nova, were used to develop design criteria for a ``fail-safe`` lens (that may catastrophically fracture but not implode). Specifically, the window must be made thick enough so that the peak tensile stress is less than 500 psi (3.4 MPa) and the thickness/critical flaw size is less than 6. The air leak through the window fracture and into the vacuum must be rapid enough to reduce the load on the window before secondary crack growth occurs. Finite element stress calculations of a window before and immediately following fracture into two pieces show that the elastic stored energy is redistributed if the fragments ``lock`` in place and thereby bridge the opening. In such cases, the peak stresses at the flaw site can increase, leading to further (i.e. secondary) crack growth.

Campbell, J.H.; Hurst, P.A.; Heggins, D.D.; Steele, W.A.; Bumpas, S.E.

1996-11-01

283

Study of Bacterial Samples Using Laser Induced Breakdown Spectroscopy  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) technique has been applied to investigate two different types of bacteria, Escherichia coli (B1) and Micrococcus luteus (B2) deposited on glass slides using Spectrolaser 7000. LIBS spectra were analyzed using spectrolaser software. LIBS spectrum of glass substrate was compared with bacteria spectra. Ca, Mg, Na, K, P, S, Cl, Fe, Al, Mn, Cu, C, H and CN-band appeared in bacterial samples in air. Two carbon lines at 193.02 nm, 247.88 nm and one hydrogen line at 656.28 nm with intensity ratios of 1.9, 1.83 and 1.53 appeared in bacterial samples B1 and B2 respectively. Carbon and hydrogen are the important components of the bio-samples like bacteria and other cancer cells. Investigation on LIBS spectra of the samples in He and Ar atmospheres is also presented. Ni lines appeared only in B2 sample in Ar atmosphere. From the present experimental results we are able to show that LIBS technique has a potential in the identification and discrimination of different types of bacteria.

W, A. Farooq; M, Atif; W, Tawfik; M, S. Alsalhi; Z, A. Alahmed; M, Sarfraz; J, P. Singh

2014-12-01

284

Laser-induced focused ultrasound for nondestructive testing and evaluation  

NASA Astrophysics Data System (ADS)

Focused ultrasound pulses generated by photoacoustic transformation at a metal surface immersed in water possess a pronounced compression phase on the nanosecond time scale. For 8 ns laser pump pulses, the spectrum of the initially generated ultrasonic pulse covered a frequency range between 0.1 and 150 MHz. A concave spherical geometry of the light-absorbing metal surface can be used to achieve focusing. In the present experiments a conical ultrasound beam was directed at a solid glass plate or silicon wafer, where the tilt of the normal of the metal mirror defined the efficiency of mode conversion at the water-solid interface. Depending on the configuration, focused bulk waves as well as Rayleigh and Lamb waves could be launched in the sample with this setup. The laser probe-beam-deflection method was employed for local detection of elastic disturbances at the sample surface. Due to the nonlinear elastic response of water and harmonics generation, frequencies >100 MHz were realized, despite a strong attenuation in this frequency range. Gradual increase of the laser power density from 5 to 14 MW/cm2 led to shock formation in the compressive pressure pulse in water and shortening of the Rayleigh pulse induced at the surface of the glass plate. The observed transient surface profiles were highly sensitive to nearby mechanical discontinuities such as a microcrack in glass or an edge discontinuity in silicon. Therefore, laser-induced focused ultrasound seems to be a very promising method of accomplishing diverse tasks of nondestructive evaluation.

Kozhushko, Victor V.; Hess, Peter

2008-06-01

285

Elemental analysis of cotton by laser-induced breakdown spectroscopy  

SciTech Connect

Laser-induced breakdown spectroscopy (LIBS) has been applied to the elemental characterization of unprocessed cotton. This research is important in forensic and fraud detection applications to establish an elemental fingerprint of U.S. cotton by region, which can be used to determine the source of the cotton. To the best of our knowledge, this is the first report of a LIBS method for the elemental analysis of cotton. The experimental setup consists of a Nd:YAG laser that operates at the fundamental wavelength as the LIBS excitation source and an echelle spectrometer equipped with an intensified CCD camera. The relative concentrations of elements Al, Ba, Ca, Cr, Cu, Fe, Mg, and Sr from both nutrients and environmental contributions were determined by LIBS. Principal component analysis was used to visualize the differences between cotton samples based on the elemental composition by region in the U.S. Linear discriminant analysis of the LIBS data resulted in the correct classification of >97% of the cotton samples by U.S. region and >81% correct classification by state of origin.

Schenk, Emily R.; Almirall, Jose R.

2010-05-01

286

Airborne laser induced fluorescence imaging. Innovative technology summary report  

SciTech Connect

Laser-Induced Fluorescence (LIF) was demonstration as part of the Fernald Environmental Management Project (FEMP) Plant 1 Large Scale Demonstration and Deployment Project (LSDDP) sponsored by the US Department of Energy (DOE) Office of Science and Technology, Deactivation and Decommissioning Focus Area located at the Federal Energy Technology Center (FETC) in Morgantown, West Virginia. The demonstration took place on November 19, 1996. In order to allow the contaminated buildings undergoing deactivation and decommissioning (D and D) to be opened to the atmosphere, radiological surveys of floors, walls and ceilings must take place. After successful completion of the radiological clearance survey, demolition of the building can continue. Currently, this process is performed by collecting and analyzing swipe samples for radiological analysis. Two methods are used to analyze the swipe samples: hand-held frisker and laboratory analysis. For the purpose of this demonstration, the least expensive method, swipe samples analyzed by hand-held frisker, is the baseline technology. The objective of the technology demonstration was to determine if the baseline technology could be replaced using LIF.

NONE

1999-06-01

287

Ophthalmic manifestations of laser-induced eye injuries  

NASA Astrophysics Data System (ADS)

The basis for almost all laser-induced eye injuries is the concentration of the radiation in the visible and near infra red range on the retina. The effect of this concentration is that the energy required to produce a visible retinal lesion is minuscule, about 50 microjoule for a Q- switched 532 nm laser. Even at lower energies the radiation can cause dazzle and flash blindness. At higher energies it can produce lesions which are ophthalmoscopically invisible, and at even higher energies, lesions that are visible and permanent. Higher energies still produce vitreous hemorrhage. The functional results of visible lesions depend not only on the energy impinging on the retina but mostly on the location of the injury. Foveal lesions will cause permanent reduction in visual functions, extrafoveal injuries will cause temporary visual incapacitation, and lesions further away from the macula may cause unnoticeable damage. Temporary incapacitation by intraocular hemorrhage can be engendered by a lesion anywhere in the eye. The latter is usually absorbed spontaneously or can be surgically removed by vitrectomy. An over-threshold injury anywhere on the posterior pole of the eye will lead to severance of the retinal nerve fiber layer, and thus to blind spots in parts of the retina unaffected by the original lesion. A common late, visually devastating, effect of laser lesions is retinal scarring which may lead to retinal holes, retinal detachment and delayed blindness.

Belkin, Michael

1996-04-01

288

Intraoperative metastases detection by laser-induced fluorescence spectroscopy  

NASA Astrophysics Data System (ADS)

The authors studied the ability of Laser Induced Fluorescence Spectroscopy (LIFS) for the intraoperative identification of metastases using a photosensitizing agent Photofrin IIr to enhance spectroscopic detection. A He-Cd laser source (442 nm) was used to produce low-power illumination of tissue via a hand-held 400 micrometers fiberoptic probe. Through the same fiber, reflected and emitted light was returned to an optical multi-channel analyzer (OMA III) for analysis. Spectroscopic signals were displayed on a screen for immediate examination. Lobund Wistar rats, inoculated with Pollard rat adenocarcinoma cells, were used as an animal model. Photofrin IIr was administered intraperitoneal 24 or 48 hours prior to surgical exploration in doses varying from 0.75-7.5 mg/kg. Metastases detection was performed during abdominal exploration directed to ipsilateral and contralateral inguinal, iliac, para-aortic and renal lymph nodes. Nineteen tissue samples, identified as abnormal by LIFS, were removed for histologic analysis; 11 of these samples were larger than 5mm and histologic examination revealed malignancy in all cases. While LIFS signals showed malignancy in 8 tissue samples with dimensions less than 5mm, histology confirmed this in only 3. However, serial histologic sections were not performed. From the initial results, it was concluded that LIFS detection of malignant tissue is feasible and enhanced by the addition of Photofrin IIr. LIFS may be a promising technique for the intraoperative detection of primary malignant and metastatic tissue.

Vari, Sandor G.; Papazoglou, Theodore G.; van der Veen, Maurits J.; Fishbein, Michael C.; Young, J. D.; Chandra, Mudjianto; Papaioannou, Thanassis; Beeder, Clain; Shi, Wei-Qiang; Grundfest, Warren S.

1991-06-01

289

Simultaneous elemental analysis system using laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

A new instrumentation variation on laser induced breakdown spectroscopy (LIBS) is presented that allows simultaneous determination of all detectable elements using a multiple spectrograph and synchronous, multiple charge coupled device spectral acquisition system. The device has been designed to reduce the cost penalties often associated with the application of LIBS while allowing accurate and precise determination of the elemental composition of bulk materials. The system is particularly suited to the analysis of heterogeneous materials such as coal and mineral ores. In coal analysis detectable elements include the key inorganic components of coal—such as Al, Si, Mg, Ca, Fe, Na, and K—in addition to C and H. Detection limits vary depending on the particular element, but are typically of the order of 0.01% for as received, moist materials. Measurement repeatability and accuracy are typically within ±10% absolute, which is similar to results from standard analysis procedures for heterogeneous materials. Beta versions of the device have been produced and are currently being used routinely in two commercial coal-fired power stations.

Body, Doug; Chadwick, Bruce L.

2001-03-01

290

Laser-induced breakdown spectroscopy in industrial and security applications  

SciTech Connect

Laser-induced breakdown spectroscopy (LIBS) offers rapid, localized chemical analysis of solid or liquid materials with high spatial resolution in lateral and depth profiling, without the need for sample preparation. Principal component analysis and partial least squares algorithms were applied to identify a variety of complex organic and inorganic samples. This work illustrates how LIBS analyzers can answer a multitude of real-world needs for rapid analysis, such as determination of lead in paint and children's toys, analysis of electronic and solder materials, quality control of fiberglass panels, discrimination of coffee beans from different vendors, and identification of generic versus brand-name drugs. Lateral and depth profiling was performed on children's toys and paint layers. Traditional one-element calibration or multivariate chemometric procedures were applied for elemental quantification, from single laser shot determination of metal traces at {approx}10 {mu}g/g to determination of halogens at 90 {mu}g/g using 50-shot spectral accumulation. The effectiveness of LIBS for security applications was demonstrated in the field by testing the 50-m standoff LIBS rasterizing detector.

Bol'shakov, Alexander A.; Yoo, Jong H.; Liu Chunyi; Plumer, John R.; Russo, Richard E.

2010-05-01

291

Laser-induced backside wet cleaning technique for glass substrates  

NASA Astrophysics Data System (ADS)

The aim of this paper is to study the laser-induced backside wet cleaning techniques for glass substrates. Two kinds of laser cleaning techniques are proposed in this study. The first involves applying an Nd:YAG laser to the backside of the substrate which is submerged in water. A metal plate is placed below the glass substrate. Most of the laser energy will be absorbed by the metal plate. The metal then vaporizes the water and generates a turbulent bubble flow. The bubble flow removes the alumina particles from the surface of the glass substrate. The second involves using a CO2 laser to generate turbulent bubble flow to remove the particles. Both methods were successfully demonstrated for the removal of submicron particles of 0.5 ?m in size. The phenomena of bubble generation and diffusion are presented in the paper. Because the laser is applied to the backside of the substrate, the damage due to the laser heat can be significantly reduced. The quality and efficient of the backside processing is better than those of the front side processing. The proposed techniques have great potential to provide an improved solution for glass cleaning.

Weng, Tsu-Shien; Tsai, Chwan-Huei

2014-08-01

292

Discrimination of forensic trace evidence using laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Elemental analysis in forensic laboratories can be tedious and many trace evidence items are not analyzed to determine their elemental composition. Presently, scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS) is the primary analytical tool for determining the elemental composition of trace evidence items. However, due to the time it takes to obtain the required vacuum and the limited number of samples that can be analyzed at any one time, SEM-EDS can be impractical for a high volume of evidence items. An alternative instrument that can be used for this type of analysis is laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). While LA-ICP-MS is a very precise and quantitative analytical method that determines elemental composition based on isotopic mass measurements; however, the instrumentation is relatively expensive and therefore is budgetarily prohibitive for many forensic laboratories. It is the purpose of this research to evaluate an inexpensive instrument that can potentially provide rapid elemental analysis for many forensic laboratories. Laser induced breakdown spectroscopy (LIBS) is an analytical method that meets these requirements and offers information about the elemental composition based on ionic, atomic and diatomic molecular emissions.

Bridge, Candice Mae

293

Treatment of laser-induced retinal injuries by neuroprotection  

NASA Astrophysics Data System (ADS)

Retinal laser photocoagulation treatments are often complicated with immediate side-effect of visual impairment. To determine whether glutamate-receptor blockers can serve as adjuvant neuroprotective therapy, we examined the effect of MK-801, an NMDA-receptor antagonist, on laser-induced retinal injury in a rat model. Argon laser retinal lesions were created in the retina of 36 DA rats. Treatment with intraperitoneal injections of MK-801 or saline was started immediately after the laser photocoagulation. The animals were sacrificed after 3, 20 or 60 days and the retinal lesions were evaluated histologically and morphometrically. Photoreceptor-cell loss was significantly smaller in MK-801-treated rats than controls. The proliferative membrane composed of retinal pigment epithelial cells which was seen at the base of the lesion in control retinas, was smaller in the MK-801-treated retinas. MK-801 exhibited neuroprotective and anti-proliferative properties in the retina. Glutamate-receptor blockers should be further investigated for serving as adjuvant therapy to retinal photocoagulation treatments.

Solberg, Yoram; Rosner, Mordechai; Belkin, Michael

1997-05-01

294

Laser-induced incandescence measurements of particles in aeroengine exhausts  

NASA Astrophysics Data System (ADS)

Laser Induced Incandescence (LII) has been demonstrated as a non-intrusive technique for measurement of particle concentration in the exhausts of aero-engines on sea level test beds as part of a European Union collaborative program (AEROJET) aimed at replacing gas sampling rakes behind development engines with non-intrusive instrumentation. Currently emissions of CO, NOx, unburned hydrocarbon, and smoke from aero-engines must be shown to be less than internationally specified limits. Measurements are made on development engines on sea level test beds by applying a number of standard analytical methods to extracted exhaust gas samples. The hardware required for exhaust gas sampling is heavy and complex and is expensive to build and install. As a result, only the minimum number of emissions tests are conducted during an engine development program, and emissions data is only available to combustion engineers late in the program. Hence, there is a need for more versatile and less costly non-intrusive measurement techniques. Molecular species can be measured using Fourier Transform Infrared (FTIR) spectroscopy, while LII is a promising smoke measuring technique. The development of an LII system specifically designed for exhaust applications is described.

Black, John D.

1999-09-01

295

Laser-induced electron diffraction for probing rare gas atoms.  

PubMed

Recently, using midinfrared laser-induced electron diffraction (LIED), snapshots of a vibrating diatomic molecule on a femtosecond time scale have been captured [C.I. Blaga et al., Nature (London) 483, 194 (2012)]. In this Letter, a comprehensive treatment for the atomic LIED response is reported, a critical step in generalizing this imaging method. Electron-ion differential cross sections (DCSs) of rare gas atoms are extracted from measured angular-resolved, high-energy electron momentum distributions generated by intense midinfrared lasers. Following strong-field ionization, the high-energy electrons result from elastic rescattering of a field-driven wave packet with the parent ion. For recollision energies ?100 eV, the measured DCSs are indistinguishable for the neutral atoms and ions, illustrating the close collision nature of this interaction. The extracted DCSs are found to be independent of laser parameters, in agreement with theory. This study establishes the key ingredients for applying LIED to femtosecond molecular imaging. PMID:23368191

Xu, Junliang; Blaga, Cosmin I; DiChiara, Anthony D; Sistrunk, Emily; Zhang, Kaikai; Chen, Zhangjin; Le, Anh-Thu; Morishita, Toru; Lin, C D; Agostini, Pierre; DiMauro, Louis F

2012-12-01

296

Hyperspectral laser-induced autofluorescence imaging of dental caries  

NASA Astrophysics Data System (ADS)

Dental caries is a disease characterized by demineralization of enamel crystals leading to the penetration of bacteria into the dentine and pulp. Early detection of enamel demineralization resulting in increased enamel porosity, commonly known as white spots, is a difficult diagnostic task. Laser induced autofluorescence was shown to be a useful method for early detection of demineralization. The existing studies involved either a single point spectroscopic measurements or imaging at a single spectral band. In the case of spectroscopic measurements, very little or no spatial information is acquired and the measured autofluorescence signal strongly depends on the position and orientation of the probe. On the other hand, single-band spectral imaging can be substantially affected by local spectral artefacts. Such effects can significantly interfere with automated methods for detection of early caries lesions. In contrast, hyperspectral imaging effectively combines the spatial information of imaging methods with the spectral information of spectroscopic methods providing excellent basis for development of robust and reliable algorithms for automated classification and analysis of hard dental tissues. In this paper, we employ 405 nm laser excitation of natural caries lesions. The fluorescence signal is acquired by a state-of-the-art hyperspectral imaging system consisting of a high-resolution acousto-optic tunable filter (AOTF) and a highly sensitive Scientific CMOS camera in the spectral range from 550 nm to 800 nm. The results are compared to the contrast obtained by near-infrared hyperspectral imaging technique employed in the existing studies on early detection of dental caries.

Bürmen, Miran; Fidler, Aleš; Pernuš, Franjo; Likar, Boštjan

2012-01-01

297

Stimulated laser induced fluorescence holography for imaging fluorescent species  

NASA Astrophysics Data System (ADS)

In this paper pulsed digital holographic detection is coupled to the stimulated laser induced fluorescence (LIF) effect for imaging fluorescent species. A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent resulting in a gain through stimulated emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to stimulated fluorescence emission which is coupled to the concentration of the dye. The results show that the amplification of the probe beam (532 nm) due to stimulated LIF emission is seen in the intensity maps. The gain is about 40% at a dye concentration of 0.32 g/L and decreases to be about 20% at a dye concentration of 0.04 g/L for a probe beam energy density of 0.1 mJ/cm2. Spectroscopic measurements have been carried out to confirm the holographic results. The results show that stimulated LIF holography is a promising technique for quantitative imaging of fluorescent species.

Amer, Eynas; Gren, Per; Sjödahl, Mikael

2013-01-01

298

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

299

Time-resolved laser-induced fluorescence system  

NASA Astrophysics Data System (ADS)

Fluorescence methods are being used increasingly in the measurement of species concentrations in gases, liquids and solids. Laser induced fluorescence is spontaneous emission from atoms or molecules that have been excited by laser radiation. Here we present a time resolved fluorescence instrument that consists of a 5 ?J Nitrogen laser (337.1 nm), a sample holder, a quartz optical fiber, a spectrometer, a PMT and a PC that allows the measurement of visible fluorescence spectra (350-750 nm). Time response of the system is approximately 5 ns. The instrument has been used in the measurement of colored bond paper, antifreeze, diesel, cochineal pigment and malignant tissues. The data acquisition was achieved through computer control of a digital oscilloscope (using General Purpose Interface Bus GPIB) and the spectrometer via serial (RS232). The instrument software provides a graphic interface that lets make some data acquisition tasks like finding fluorescence spectra, and fluorescence lifetimes. The software was developed using the Lab-View 6i graphic programming package and can be easily managed in order to add more functions to it.

Bautista, F. J.; De la Rosa, J.; Gallegos, F. J.

2006-02-01

300

Laser-induced acoustic emissions in experimental dental composites.  

PubMed

A laser thermoacoustic technique was innovated to evaluate laser-induced acoustic emissions (AEs) in experimental dental composites aged with 75% ethanol solution. Experimental composite systems of 75/25 BisGMA/TEGDMA resin filled with 0, 12.6, 30.0, and 56.5 vol% of 8-microm silanized and unsilanized BaSiO6 were analyzed. The sample size was 4.65 mm (diameter) x 0.5 mm (thick). Aging effects of immersing in 75% ethanol for up to 14 h on AEs were then evaluated. A continuous-wave CO2 laser was used to heat the samples. Acoustic emissions were collected as a function of filler fraction, laser power, silanization, and immersion time. Onset of burst-pattern acoustic signals characteristic of fracturing occurred at different laser powers for different tested groups. Acoustic emissions generally increased with laser power, in which lower laser powers produced low-amplitude (45-50 dB) signals; the amplitude distribution (50-85 dB) became more extensive as laser powers increased. After immersion, the lower laser powers could produce the same phenomenon. The higher the filler fraction, the fewer AEs generated. A large percentage AE reduction due to silanization was noted as a function of filler fraction. Unsilanized specimens showed more thermal damages than did silanized ones. PMID:10850935

Lee, S Y; Lin, C T; Keh, E S; Pan, L C; Huang, H M; Shih, Y H; Cheng, H C

2000-07-01

301

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

302

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

303

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

304

Chemical characterization of single micro- and nano-particles by optical catapulting-optical trapping-laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Spectral identification of individual micro- and nano-sized particles by the sequential intervention of optical catapulting, optical trapping and laser-induced breakdown spectroscopy is presented. The three techniques are used for different purposes. Optical catapulting (OC) serves to put the particulate material under inspection in aerosol form. Optical trapping (OT) permits the isolation and manipulation of individual particles from the aerosol, which are subsequently analyzed by laser-induced breakdown spectroscopy (LIBS). Once catapulted, the dynamics of particle trapping depends both on the laser beam characteristics (power and intensity gradient) and on the particle properties (size, mass and shape). Particles are stably trapped in air at atmospheric pressure and can be conveniently manipulated for a precise positioning for LIBS analysis. The spectra acquired from the individually trapped particles permit a straightforward identification of the material inspected. Variability of LIBS signal for the inspection of Ni microspheres was 30% relative standard deviation. OC-OT-LIBS permits the separation of particles in a heterogeneous mixture and the subsequent analysis of the isolated particle of interest. In order to evaluate the sensitivity of the approach, the number of absolute photons emitted by a single trapped particle was calculated. The limit of detection (LOD) for Al2O3 particles was calculated to be 200 attograms aluminium.

Fortes, Francisco J.; Fernández-Bravo, Angel; Javier Laserna, J.

2014-10-01

305

Experimental study of underwater rock drilling using a pulsed Ho:YAG laser-induced jets  

Microsoft Academic Search

This paper is primarily an assessment of laser-induced water jets for boring rock surfaces. It also reports the result of\\u000a preliminary experiments of pulsed Ho:YAG laser-induced jets applied to drill a submerged rock specimen. The irradiation of\\u000a pulsed Ho:YAG laser beams at 3 Hz inside a thin metal tube produces intermittent water vapor bubbles which result in liquid\\u000a jet discharge from

K. Ohtani; D. Numata; K. Takayama; T. Kobayashi; K. Okatsu

2009-01-01

306

Excimer-laser-induced fluorescence of rabbit cornea: radiometric measurement through the cornea  

SciTech Connect

The laser-induced fluorescence spectrum of rabbit cornea irradiated at ablative intensities was measured. This system directly measured the radiant exposure of fluorescence transmitted through the cornea when the anterior surface of the cornea was irradiated by an ArF excimer laser. Evidence of changing spectral characteristics as a function of total laser dose suggests photochemical changes in the cornea may be occurring. Results are compared with previous data of laser-induced fluorescence in other models and detection schemes.

Ediger, M.N. (Food and Drug Administration, Rockville, MD (USA))

1991-01-01

307

Laser-induced desorption from silicon (111) surfaces with adsorbed chlorine atoms  

Microsoft Academic Search

We have studied the initial stage of the laser-induced reaction of silicon surfaces with adsorbed chlorine atoms in ultrahigh vacuum, by measuring the species desorbing from the surfaces. In particular, our studies have focused on photo-chemical etching without laser-induced thermal heating. We found that the primary species desorbing from Cl-saturated Si(111) surfaces is the molecule and that the desorption efficiency

K. Hattori; K. Shudo; T. Iimori; F. Komori; Y. Murata

1996-01-01

308

Ejection of particles placed on a thin film by laser-induced forward transfer  

NASA Astrophysics Data System (ADS)

Laser-induced forward transfer (LIFT) was applied to eject the particles placed on a thin film. The behavior of the fluorescent particles in the gas phase was observed by a two-dimensional laser-induced fluorescence (2D-LIF) technique. The behavior of emissive particles was also imaged. The speed of the particles was in the order of few hundreds m/s, and changed with ablation conditions. The fastest speed was around 280 m/s.

Nakata, Yoshiki; Okada, Tatsuo; Maeda, Mitsuo

2001-06-01

309

Millimeter radio wave scattering on laser-induced discharges in a dusty atmosphere  

NASA Astrophysics Data System (ADS)

The integral absorption of millimeter radio waves in atmospheric gases on the near-ground and oblique paths with a scatterer is compared. The scattering properties of millimeter-radio waves of the plasma nimbus of the laser-induced air discharge in atmospheric aerosol are studied experimentally. It is shown that laser-induced breakdown can be used as a repeater for mm-band communication lines up to 40 km.

Kisliakov, A. G.; Kanakov, V. A.; Sorokin, Iu. M.; Finkel'Shtein, S. E.

1992-01-01

310

Laser-induced stresses versus mechanical stress power measurements during laser ablation of solids  

Microsoft Academic Search

Laser-induced stresses resulting from high-power laser-material interactions have been studied extensively. However, the rate of change in mechanical energy, or stress power, due to laser-induced stresses has only recently been investigated. An unanswered question for monitoring laser-material interactions in the far-field is whether stress power differs from stresses measured, particularly with respect to laser-energy coupling to a solid target. This

Mark A. Shannon; Richard E. Russo

1995-01-01

311

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 ft 3) 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

312

Laser-induced synergistic effects around absorbing nanoclusters in live cells  

NASA Astrophysics Data System (ADS)

Background and Objective: The application of nanotechnology for laser thermal-based killing of abnormal cells (e.g. cancer cells) targeted with absorbing nanoparticles (e.g. gold solid nanospheres, nanoshells, or rod) is becoming an extensive area of research. We develop an approach to enhance the efficiency of selective nanophotothermolysis of cancer cells through laser-induced synergistic effects around gold nanoparticles aggregated in nanoclusters on cell membrane. Study Design/Materials and Methods: A concept of selective target damages by laser-induced synergistic interaction of optical, thermal, and acoustic fields around clustered nanoparticles is presented with focus on overlapping bubbles from nanoparticles aggregated on cell's membrane. The experimental verification of this concept in vitro was performed by the use a tunable laser pulses (420-570 nm, 8-12 ns, 0.1-300 ?J, laser flux of 0.1-10 J/cm2) for irradiation of MDA-MB-231 breast cancer cells targeted with primary antibodies to which selecttively 40-nm gold nanoparticles were attached by the means of secondary antibodies. The photothermal, electron and atomic force microscopes in combination with viability test (annexin -V-Propidium iodide) were employed to study the nanoparticle's spatial organization, the dynamics of microbubble formations around the particle's clusters, and cells damage. Results: An aggregation of nanoparticles on cell membrane was observed with simultaneous increase bubble formation phenomena, and red-shifted absorption due to plasmon-plasmon resonances into nanoclusters. It led to a significant enhancement, at least two orders of magnitude, of the efficiency of selectively killing cancer cells with nanosecond laser pulses. Conclusion: Described approach allows using relatively small nanoparticles which would be easier delivery to target site with further creation of nanoclusters with larger sizes which provide more profound thermal and related phenomena leading to more efficient laser killing of cancer cells. This nanocluster model might be promising also for treatment or modification different targets (e.g. bacteria, virus, vascular lesions, fat, etc.) as well as teh use different type energy deposition (focused ultrasound, microwave, magnetic field, etc.).

Zharov, Vladimir P.; Letfullin, Renat R.; Galitovskay, Elena

2005-04-01

313

Laser-induced pattern formation in liquid sulfur. An indication of laser-induced phase transition to ordered polymer  

NASA Astrophysics Data System (ADS)

Liquid sulfur is a well-known liquid which exhibits a polymerization transition at T_p=159 °C. Recently, it was found from our experiments that such a transition can be induced below Tp through laser illumination and that an iridescent pattern appears under strong illumination with a pulsed laser of more than 60 mJ/cm2 pulse. It is proposed that the visible change in iridescence is due to a macroscopic reconstruction of laser-generated polymers and that a laser-induced phase transition takes place from a freely expanded polymer phase to an ordered polymer phase when increasing the laser illumination. To further examine this possibility, the time variation of the iridescent pattern has been fully investigated using a macro lens, a polarized microscope and an optical microscope. In an analysis of the iridescent pattern, a rapid decrease in the area was observed after an initial slow decrease, suggesting a type of phase transition. Results from the observation of a quenched sulfur sample with a polarized microscope gave evidence that the iridescent region consists of polymers. Through observation of the liquid with a microscope, a striped pattern with micrometer sized spacing was noted in the iridescent pattern. A drastic color change was observed in the pattern from its generation to its disappearance. Sample thickness dependence of the pattern was also observed. These results were well explained by assuming the self-arrangement of laser-generated colloidal polymers.

Sakaguchi, Y.; Tamura, K.

2007-04-01

314

Spherical grating spectrometers  

NASA Astrophysics Data System (ADS)

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

O'Donoghue, Darragh; Clemens, J. Christopher

2014-07-01

315

Production of aerosols by optical catapulting: Imaging, performance parameters and laser-induced plasma sampling rate  

NASA Astrophysics Data System (ADS)

Optical catapulting (OC) is a sampling and manipulation method that has been extensively studied in applications ranging from single cells in heterogeneous tissue samples to analysis of explosive residues in human fingerprints. Specifically, analysis of the catapulted material by means of laser-induced breakdown spectroscopy (LIBS) offers a promising approach for the inspection of solid particulate matter. In this work, we focus our attention in the experimental parameters to be optimized for a proper aerosol generation while increasing the particle density in the focal region sampled by LIBS. For this purpose we use shadowgraphy visualization as a diagnostic tool. Shadowgraphic images were acquired for studying the evolution and dynamics of solid aerosols produced by OC. Aluminum silicate particles (0.2-8 ?m) were ejected from the substrate using a Q-switched Nd:YAG laser at 1064 nm, while time-resolved images recorded the propagation of the generated aerosol. For LIBS analysis and shadowgraphy visualization, a Q-switched Nd:YAG laser at 1064 nm and 532 nm was employed, respectively. Several parameters such as the time delay between pulses and the effect of laser fluence on the aerosol production have been also investigated. After optimization, the particle density in the sampling focal volume increases while improving the aerosol sampling rate till ca. 90%.

Abdelhamid, M.; Fortes, F. J.; Fernández-Bravo, A.; Harith, M. A.; Laserna, J. J.

2013-11-01

316

Study on the effects of ion motion on laser-induced plasma wakes  

SciTech Connect

A 2D analytical model is presented for the generation of plasma wakes (or bubbles) with an ultra-intense laser pulse by taking into account the response of plasma ions. It is shown that the effect of ion motion becomes significant at the laser intensity exceeding 10{sup 21} W/cm{sup 2} and plasma background density below 10{sup 19} cm{sup -3}. In this regime, ion motion tends to suppress the electrostatic field induced by charge separation and makes the electron acceleration less effective. As a result, the assumption of immobile ions overestimates the efficiency of laser wake-field acceleration of electrons. Based on the analytical model, the dynamics of plasma ions in laser-induced wake field is investigated. It is found that only one bubble appears as the plasmas background density exceeds the resonant density and the deposited laser energy is concentrated into the bubble, resulting in the generation of an ion bunch with extremely high energy density.

Zhou Suyun [Institute of Modern Optical Technologies, Key Lab of Advanced Optical Manufacturing Technologies of Jiangsu Province and Key Lab of Modern Optical Technologies of Education Ministry of China, Soochow University, Suzhou 215006 (China); School of Materials Sciences and Engineering, Jiangxi Science and Technology Normal University, Nanchang 330013 (China); Yu Wei [Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, Shanghai 201800 (China); Yuan Xiao [Institute of Modern Optical Technologies, Key Lab of Advanced Optical Manufacturing Technologies of Jiangsu Province and Key Lab of Modern Optical Technologies of Education Ministry of China, Soochow University, Suzhou 215006 (China); Xu Han [National Laboratory for Parallel and Distributed Processing, School of Computer Science, National University of Defense Technology, Changsha 410073 (China); Cao, L. H.; Cai, H. B.; Zhou, C. T. [Institute of Applied Physics and Computational Mathematics, Beijing 100088 (China)

2012-09-15

317

Model-based planning and real-time predictive control for laser-induced thermal therapy  

PubMed Central

In this article, the major idea and mathematical aspects of model-based planning and real-time predictive control for laser-induced thermal therapy (LITT) are presented. In particular, a computational framework and its major components developed by authors in recent years are reviewed. The framework provides the backbone for not only treatment planning but also real-time surgical monitoring and control with a focus on MR thermometry enabled predictive control and applications to image-guided LITT, or MRgLITT. Although this computational framework is designed for LITT in treating prostate cancer, it is further applicable to other thermal therapies in focal lesions induced by radio-frequency (RF), microwave and high-intensity-focused ultrasound (HIFU). Moreover, the model-based dynamic closed-loop predictive control algorithms in the framework, facilitated by the coupling of mathematical modelling and computer simulation with real-time imaging feedback, has great potential to enable a novel methodology in thermal medicine. Such technology could dramatically increase treatment efficacy and reduce morbidity. PMID:22098360

Feng, Yusheng; Fuentes, David

2014-01-01

318

Effect of focusing conditions on laser-induced shock waves at titanium-water interface  

SciTech Connect

The spatial and temporal evolution of laser-induced shock waves at a titanium-water interface was analyzed using a beam deflection setup. The focusing conditions of the source laser were varied, and its effect onto the dynamics of shock waves was elucidated. For a tightly focused condition, the speed of the shock wave was {approx}6.4 Km/s, whereas for a defocused condition the velocities reduced to <3 km/s at the vicinity of the titanium-water interface. When the laser is focused a few millimeters above the target, i.e., within the water, the emission of dual shock waves was observed toward the rear side of the focal volume. These shock waves originate from the titanium-water interface as well as from the pure water breakdown region, respectively. The shock wave pressure is estimated from the shock wave velocity using the Newton's second law across a shock wave discontinuity. The shock wave pressure for a tightly focused condition was 18 GPa, whereas under a defocused condition the pressure experienced was {<=}1 GPa in the proximity of target.

Nath, Arpita; Khare, Alika

2011-07-01

319

Laser Induced Fluorescence For Measurement Of Lignin Concentrations In Pulping Liquors  

NASA Astrophysics Data System (ADS)

Laser excited fluorescence of pulping liquors was investigated for use in the pulp and paper industry for process measurement and control applications. Liquors from both mill and laboratory cooks were studied. A Nd-YAG pumped dye laser was used to generate the excitation wavelength of 280 nm; measurements were also performed using a commercially available fluorometer. Measurements on mill pulping liquors gave strong signals and showed changes in the fluorescence intensity during the cook. Absorption spectra of diluted mill liquor samples showed large changes during the cook. Samples from well controlled and characterized laboratory cooks showed fluorescence to be linear with concentration over two decades with an upper limit of approximately 1000 ppm dissolved lignin. At the end of these cooks a possible chemical change was indicated by an increase in the observed fluorescence intensity. Results indicate that lignin concentrations in pulping liquors can be accurately determined with fluorescence in the linear optical region over a greater dynamic range than absorption spectroscopy. Laser induced fluorescence may also provide an indication of chemical changes occurring in the lignin structure during a cook.

Horvath, J. J.; Semerjian, H. G.; Biasca, K. L.; Attala, R.

1988-11-01

320

Temperature effect on laser-induced breakdown spectroscopy spectra of molten and solid salts  

SciTech Connect

Laser-induced breakdown spectroscopy (LIBS) has been investigated as a potential analytical tool to improve operations and safeguards for electrorefiners, such as those used in processing spent nuclear fuel. This study set out to better understand the effect of sample temperature and physical state on LIBS spectra of molten and solid salts by building calibration curves of cerium and assessing self-absorption, plasma temperature, electron density, and local thermal equilibrium (LTE). Samples were composed of a LiCl–KCl eutectic salt, an internal standard of MnCl2, and varying concentrations of CeCl3 (0.1, 0.3, 0.5, 0.8, and 1.0 wt.% Ce) under different temperatures (773, 723, 673, 623, and 573 K). Analysis of salts in their molten form is preferred as plasma plumes from molten samples experienced less self-absorption, less variability in plasma temperature, and higher clearance of the minimum electron density required for local thermal equilibrium. These differences are attributed to plasma dynamics as a result of phase changes. Spectral reproducibility was also better in the molten state due to sample homogeneity.

Cynthia Hanson; Supathorn Phongikaroon; Jill R. Scott

2014-07-01

321

Laser-induced charge-disproportionated metallic state in LaCoO3  

NASA Astrophysics Data System (ADS)

Understanding the origin of the spin transition in LaCoO3 is one of the long-standing aims in condensed matter physics. Aside from its fundamental interest, a detailed description of this crossover will have a direct impact on the interpretation of the semiconductor-to-metal transition (SMT) and the properties of the high-temperature metallic phase in this compound, which has shown to have important applications in environmentally friendly energy production. To date, the spin transition has been investigated mainly as a function of temperature in thermal equilibrium. These results have hinted at dynamical effects. In this paper, we have investigated the SMT by means of pump-probe soft x-ray reflectivity experiments at the O K , Co L , and La M edges and theoretical calculations within a DFT++ formalism. The results point towards a laser-induced metallization in which the optical transitions stabilize a metallic state with high-spin configuration and increased charge disproportionation.

Izquierdo, M.; Karolak, M.; Trabant, C.; Holldack, K.; Föhlisch, A.; Kummer, K.; Prabhakaran, D.; Boothroyd, A. T.; Spiwek, M.; Belozerov, A.; Poteryaev, A.; Lichtenstein, A.; Molodtsov, S. L.

2014-12-01

322

Microanalysis of tool steel and glass with laser-induced breakdown spectroscopy.  

PubMed

A laser microscope system for the microanalytical characterization of complex materials is described. The universal measuring principle of laser-induced breakdown spectroscopy (LIBS) in combination with echelle optics permits a fast simultaneous multielement analysis with a possible spatial resolution below 10 pm. The developed system features completely UV-transparent optics for the laser-microscope coupling and the emission beam path and enables parallel signal detection within the wavelength range of 200-800 nm with a spectral resolution of a few picometers. Investigations of glass defects and tool steels were performed. The characterization of a glass defect in a tumbler by a micro-LIBS line scan, with use of a 266-nm diode-pumped Nd:YAG laser for excitation, is possible by simple comparison of plasma spectra of the defect and the surrounding area. Variations in the main elemental composition as well as impurities by trace elements are detected at the same time. Through measurement of the calibration samples with the known concentration of the corresponding element, a correlation between the intensity of spectral lines and the element concentration was also achieved. The change of elemental composition at the transient stellite solder of tool steels has been determined by an area scan. The two-dimensional pictures show abrupt changes of the element distribution along the solder edge and allow fundamental researches of dynamic modifications (e.g., diffusion) in steel. PMID:14594080

Loebe, Klaus; Uhl, Arnold; Lucht, Hartmut

2003-10-20

323

Microanalysis of tool steel and glass with laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

A laser microscope system for the microanalytical characterization of complex materials is described. The universal measuring principle of laser-induced breakdown spectroscopy (LIBS) in combination with echelle optics permits a fast simultaneous multielement analysis with a possible spatial resolution below 10 pm. The developed system features completely UV-transparent optics for the laser-microscope coupling and the emission beam path and enables parallel signal detection within the wavelength range of 200-800 nm with a spectral resolution of a few picometers. Investigations of glass defects and tool steels were performed. The characterization of a glass defect in a tumbler by a micro-LIBS line scan, with use of a 266-nm diode-pumped Nd:YAG laser for excitation, is possible by simple comparison of plasma spectra of the defect and the surrounding area. Variations in the main elemental composition as well as impurities by trace elements are detected at the same time. Through measurement of the calibration samples with the known concentration of the corresponding element, a correlation between the intensity of spectral lines and the element concentration was also achieved. The change of elemental composition at the transient stellite solder of tool steels has been determined by an area scan. The two-dimensional pictures show abrupt changes of the element distribution along the solder edge and allow fundamental researches of dynamic modifications (e.g., diffusion) in steel.

Loebe, Klaus; Uhl, Arnold; Lucht, Hartmut

2003-10-01

324

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

1998-01-01

325

Spectrally resolved laser-induced fluorescence for bioaerosols standoff detection  

NASA Astrophysics Data System (ADS)

An efficient standoff biological warfare detection capability could become an important asset for both defence and security communities based on the increasing biological threat and the limits of the presently existing protection systems. Defence R&D Canada (DRDC) has developed, by the end of the 90s, a standoff bioaerosol sensor prototype based on intensified range-gated spectrometric detection of Laser Induced Fluorescence (LIF). This LIDAR system named SINBAHD monitors the spectrally resolved LIF originating from inelastic interactions with bioaerosols present in atmospheric cells customizable in size and in range. SINBAHD has demonstrated the capability of near real-time detection and classification of bioaerosolized threats at multi-kilometre ranges. In spring 2005, DRDC has initiated the BioSense demonstration project, which combines the SINBAHD technology with a geo-referenced Near InfraRed (NIR) LIDAR cloud mapper. SINBAHD is now being used to acquire more signatures to add in the spectral library and also to optimize and test the new BioSense algorithm strategy. In September 2006, SINBAHD has participated in a two-week trial held at DRDC-Suffield where different open-air wet releases of live and killed bioagent simulants, growth media and obscurants were performed. An autoclave killing procedure was performed on two biological materials (Bacillus subtilis var globigii or BG, and Bacillus thuringiensis or Bt) before being aerosolized, disseminated and spectrally characterized with SINBAHD. The obtained results showed no significant impact of this killing process on their normalised spectral signature in comparison with their live counterparts. Correlation between the detection signals from SINBAHD, an array of slit samplers and a FLuorescent Aerosol Particle Sensor (C-FLAPS) was obtained and SINBAHD's sensitivity could then be estimated. At the 2006 trial, a detection limit of a few tens of Agent Containing Particles per Liter of Air (ACPLA) was obtained for a 15-m thick cloud of live BG located at a range of 400 m.

Buteau, Sylvie; Stadnyk, Laurie; Rowsell, Susan; Simard, Jean-Robert; Ho, Jim; Déry, Bernard; McFee, John

2007-09-01

326

Characterisation of CFRP surface contamination by laser induced fluorescence  

NASA Astrophysics Data System (ADS)

The application of Carbon Fibre Reinforced Polymers (CFRP) in aeronautics has been increasing. The CFRP elements are joint using rivets and adhesive bonding. The reliability of the bonding limits the use of adhesive bonding for primary aircraft structures, therefore it is important to assess the bond quality. The performance of adhesive bonds depends on the physico-chemical properties of the adhered surfaces. This research is focused on characterization of surfaces before bonding. In-situ examination of large surface materials, determine the group of methods that are preferred. The analytical methods should be non-destructive, enabling large surface analysis in relatively short time. In this work a spectroscopic method was tested that can be potentially applied for surface analysis. Four cases of surface condition were investigated that can be encountered either in the manufacturing process or during aircraft service. The first case is related to contamination of CFRP surface with hydraulic fluid. This fluid reacts with water forming a phosphoric acid that can etch the CFRP. Second considered case was related to silicone-based release agent contamination. These agents are used during the moulding process of composite panels. Third case involved moisture content in CFRP. Moisture content lowers the adhesion quality and leads to reduced performance of CFRP resulting in reduced performance of the adhesive bond. The last case concentrated on heat damage of CFRP. It was shown that laser induced fluorescence method can be useful for non-destructive evaluation of CFRP surface and some of the investigated contaminants can be easily detected.

Malinowski, Pawel H.; Sawczak, Miroslaw; Wandowski, Tomasz; Ostachowicz, Wieslaw M.; Cenian, Adam

2014-03-01

327

Laser-induced growth of nanocrystals embedded in porous materials  

PubMed Central

Space localization of the linear and nonlinear optical properties in a transparent medium at the submicron scale is still a challenge to yield the future generation of photonic devices. Laser irradiation techniques have always been thought to structure the matter at the nanometer scale, but combining them with doping methods made it possible to generate local growth of several types of nanocrystals in different kinds of silicate matrices. This paper summarizes the most recent works developed in our group, where the investigated nanoparticles are either made of metal (gold) or chalcogenide semiconductors (CdS, PbS), grown in precursor-impregnated porous xerogels under different laser irradiations. This review is associated to new results on silver nanocrystals in the same kind of matrices. It is shown that, depending on the employed laser, the particles can be formed near the sample surface or deep inside the silica matrix. Photothermal and/or photochemical mechanisms may be invoked to explain the nanoparticle growth, depending on the laser, precursor, and matrix. One striking result is that metal salt reduction, necessary to the production of the corresponding nanoparticles, can efficiently occur due to the thermal wrenching of electrons from the matrix itself or due to multiphoton absorption of the laser light by a reducer additive in femtosecond regime. Very localized semiconductor quantum dots could also be generated using ultrashort pulses, but while PbS nanoparticles grow faster than CdS particles due to one-photon absorption, this better efficiency is counterbalanced by a sensitivity to oxidation. In most cases where the reaction efficiency is high, particles larger than the pores have been obtained, showing that a fast diffusion of the species through the interconnected porosity can modify the matrix itself. Based on our experience in these techniques, we compare several examples of laser-induced nanocrystal growth in porous silica xerogels, which allows extracting the best experimental conditions to obtain an efficient particle production and to avoid stability or oxidation problems. PMID:23742134

2013-01-01

328

Laser induced spark ignition of methane-oxygen mixtures  

NASA Technical Reports Server (NTRS)

Results from an experimental study of laser induced spark ignition of methane-oxygen mixtures are presented. The experiments were conducted at atmospheric pressure and 296 K under laminar pre-mixed and turbulent-incompletely mixed conditions. A pulsed, frequency doubled Nd:YAG laser was used as the ignition source. Laser sparks with energies of 10 mJ and 40 mJ were used, as well as a conventional electrode spark with an effective energy of 6 mJ. Measurements were made of the flame kernel radius as a function of time using pulsed laser shadowgraphy. The initial size of the spark ignited flame kernel was found to correlate reasonably well with breakdown energy as predicted by the Taylor spherical blast wave model. The subsequent growth rate of the flame kernel was found to increase with time from a value less than to a value greater than the adiabatic, unstretched laminar growth rate. This behavior was attributed to the combined effects of flame stretch and an apparent wrinkling of the flame surface due to the extremely rapid acceleration of the flame. The very large laminar flame speed of methane-oxygen mixtures appears to be the dominant factor affecting the growth rate of spark ignited flame kernels, with the mode of ignition having a small effect. The effect of incomplete fuel-oxidizer mixing was found to have a significant effect on the growth rate, one which was greater than could simply be accounted for by the effect of local variations in the equivalence ratio on the local flame speed.

Santavicca, D. A.; Ho, C.; Reilly, B. J.; Lee, T.-W.

1991-01-01

329

Experimental study of the spectral characteristics of laser-induced air plasma  

SciTech Connect

The characteristics of laser-induced air, N2, and O2 plasma spectra are investigated spectroscopically. The study concentrates mainly on the temporal behavior of laser-induced plasma after breakdown. We used delayed spectra and spectra evolution for this study. Except for the general one-beam laser-induced breakdown experiment, a second laser beam was added to further probe the behavior of plasma during its decay. We report the experimental results of spectra composition, spectra time evolution, and spectra affected by a second laser beam. We determined that all the laser-induced air plasma spectra are from a continuous spectrum and some line spectra superposed on the continuous spectrum. The stronger short wavelength continuous spectrum is caused by bremsstrahlung radiation of electrons in the plasma, and the weaker long wavelength continuous spectrum is caused by electron and ion recombination. Line spectra originate from excited molecules, atoms, and their first-order ions, but no line spectra form higher-order ions. The results show that the temporal behavior of some spectra is a decay-rise-redecay pattern. With the two laser beam experiment we found that all the spectra intensities are enhanced by the second laser beam, but the response of various spectra to the delay of the second laser beam is quite different, in particular, the intensity increments of some spectra increase with the delay of the second laser beam. Some microscopic processes of laser-induced plasma obtained from the experimental results are discussed. These results are useful for a better understanding of some laser-induced air plasma related applications, such as laser-guided lightning and laser-induced breakdown spectroscopy.

Lin Zhaoxiang; Wu Jinquan; Sun Fenglou; Gong Shunsheng

2010-05-01

330

Suppression of laser-induced choroidal neovascularization by intravitreal injection of tristetraprolin  

PubMed Central

AIM To examine the effect of intravitreal adenoviral vector-mediated tristetraprolin (Ad-TTP) on VEGF mRNA expression in a rat model of laser-induced choroidal neovascularization. METHODS Ad-TTP was prepared using a commercial kit. Retinal laser-induced photocoagulation (10 spots per eye) was performed on rats in this experimental choroidal neovascularization (CNV) model. Rats were divided into four groups: control (single intravitreal injection of balanced salt solution, n=10), laser-induced CNV (photocoagulation only, n=20), laser-induced CNV plus Ad-TTP injection (photocoagulation plus a single intravitreal Ad-TTP injection, n=20) and Ad-TTP injection only (n=10). Changes in choroidal morphology were evaluated in ten rats in the laser only and the laser plus Ad-TTP groups. Two weeks after laser injury, the size of CNV was calculated by perfusion with high-molecular-weight fluorescein isothiocyanate (FITC)-dextran. VEGF mRNA expression in retina-choroid tissue from ten rats in each group was measured by reverse transcription polymerase chain reaction (RT-PCR). RESULTS Two weeks after treatment, the area of laser-induced CNV was reduced by approximately 60% in the rats given the Ad-TTP injection compared with that in the laser-only group. There was a tendency toward decreased VEGF mRNA expression in the Ad-TTP injection groups. CONCLUSION A single intravitreal injection of Ad-TTP significantly suppressed CNV size in this experimental laser-induced CNV model. Ad-TTP injection also decreased VEGF mRNA expression compared with that in the laser-induced CNV group. The present study is meaningful as the first study to investigate the effect of tristetraprolin delivered via intravitreal injection.

Cho, Yong Wun; Han, Yong Seop; Chung, In Young; Kim, Seong Jae; Seo, Seong Wook; Yoo, Ji Myong; Park, Jong Moon

2014-01-01

331

Superfluid {sup 4}He Quantum Interference Grating  

SciTech Connect

We report the first observation of quantum interference from a grating structure consisting of four weak link junctions in superfluid {sup 4}He. We find that an interference grating can be implemented successfully in a superfluid matter wave interferometer to enhance its sensitivity while trading away some of its dynamic range. We also show that this type of device can be used to measure absolute quantum mechanical phase differences. The results demonstrate the robust nature of superfluid phase coherence arising from quantum mechanics on a macroscopic scale.

Sato, Yuki; Joshi, Aditya; Packard, Richard [Physics Department, University of California, Berkeley, California 94720 (United States)

2008-08-22

332

Reaction Dynamics of Halorhodopsin Studied by Time-Resolved Diffusion  

PubMed Central

Reaction dynamics of a chloride ion pump protein, halorhodopsin (HR), from Natronomonas pharaonis (N. pharaonis) (NpHR) was studied by the pulsed-laser-induced transient grating (TG) method. A detailed investigation of the TG signal revealed that there is a spectrally silent diffusion process besides the absorption-observable reaction dynamics. We interpreted these dynamics in terms of release, diffusion, and uptake of the Cl? ion. From a quantitative global analysis of the signals at various grating wavenumbers, it was concluded that the release of the Cl? ion is associated with the L2 ? (L2 (or N) ? O) process, and uptake of Cl? occurs with the (L2 (or N) ? O) ? NpHR? process. The diffusion coefficient of NpHR solubilized in a detergent did not change during the cyclic reaction. This result contrasts the behavior of many photosensor proteins and implies that the change in the H-bond network from intra- to intermolecular is not significant for the activity of this protein pump. PMID:19413978

Inoue, Keiichi; Kubo, Megumi; Demura, Makoto; Kamo, Naoki; Terazima, Masahide

2009-01-01

333

Aerosol beam-focus laser-induced plasma spectrometer device  

DOEpatents

An apparatus for detecting elements in an aerosol includes an aerosol beam focuser for concentrating aerosol into an aerosol beam; a laser for directing a laser beam into the aerosol beam to form a plasma; a detection device that detects a wavelength of a light emission caused by the formation of the plasma. The detection device can be a spectrometer having at least one grating and a gated intensified charge-coupled device. The apparatus may also include a processor that correlates the wavelength of the light emission caused by the formation of the plasma with an identity of an element that corresponds to the wavelength. Furthermore, the apparatus can also include an aerosol generator for forming an aerosol beam from bulk materials. A method for detecting elements in an aerosol is also disclosed.

Cheng, Meng-Dawn (Oak Ridge, TN)

2002-01-01

334

Analysis of metallic multilayers using hypersonic surface waves induced by transient reflecting gratings  

NASA Astrophysics Data System (ADS)

Gigahertz surface accoustic waves (the Rayleigh-like modes) have been optically generated and detected on ultrathin (less than 1 micron) metallic single-layer and multilayered films attached to glass substrates using the laser-induced transient reflecting grating (TRG) technique. The dispersion relations of the excited Rayleigh-like modes could be constructed experimentally and theoretically. By finding the best fitting of the theoretical dispersion curves to the experimental data, this method can be used to deduce the elastic constants of ultrathin multilayered films.

Shen, Qing; Harat, Akira; Sawada, Tsuguo

1993-08-01

335

Laser-Induced Thermal Acoustic Measurements in a Highly Back-Pressured Scramjet Isolator Model: A Research Plan  

NASA Technical Reports Server (NTRS)

Under the Propulsion Discipline of NASA s Fundamental Aeronautics Program s Hypersonics Project, a test apparatus, for testing a scramjet isolator model, is being constructed at NASA's Langley Research Center. The test apparatus will incorporate a 1-inch by 2-inch by 15-inch-long scramjet isolator model supplied with 2.1 lbm/sec of unheated dry air through a Mach 2.5 converging-diverging nozzle. The planned research will incorporate progressively more challenging measurement techniques to characterize the flow field within the isolator, concluding with the application of the Laser-Induced Thermal Acoustic (LITA) measurement technique. The primary goal of this research is to use the data acquired to validate Computational Fluid Dynamics (CFD) models employed to characterize the complex flow field of a scramjet isolator. This paper describes the test apparatus being constructed, pre-test CFD simulations, and the LITA measurement technique.

Middleton, Troy F.; Balla, Robert J.; Baurle, Robert A.; Wilson, Lloyd G.

2008-01-01

336

Time-Resolved Visualization of Laser-Induced Heating of Gold with MeV Ultrafast Electron Diffraction  

NASA Astrophysics Data System (ADS)

Time-resolved electron diffraction employing MeV electron beams is demonstrated experimentally at the center for ultrafast diffraction and microscopy of Shanghai Jiao Tong University. A high-quality diffraction pattern is recorded by a single shot of electron pulse. Synchronization between the pump laser and the probe electron beam is achieved through measurement of electron deflection caused by the laser-induced plasmas in a metal tip. We study the ultrafast structural dynamics of the gold lattice excited by a femtosecond laser through tracing the change of Bragg peaks intensity at different time delays. It is expected that the combination of MeV ultrashort electron beams and femtosecond laser pulses will open many new opportunities in the ultrafast and ultrasmall world.

Zhu, Peng-Fei; Fu, Fei-Chao; Liu, Sheng-Guang; Xiang, Dao; Zhang, Jie; Cao, Jian-Ming

2014-11-01

337

In situ nanoparticle size measurements of gas-borne silicon nanoparticles by time-resolved laser-induced incandescence  

NASA Astrophysics Data System (ADS)

This paper describes the application of time-resolved laser-induced incandescence (TiRe-LII), a combustion diagnostic used mainly for measuring soot primary particles, to size silicon nanoparticles formed within a plasma reactor. Inferring nanoparticle sizes from TiRe-LII data requires knowledge of the heat transfer through which the laser-heated nanoparticles equilibrate with their surroundings. Models of the free molecular conduction and evaporation are derived, including a thermal accommodation coefficient found through molecular dynamics. The model is used to analyze TiRe-LII measurements made on silicon nanoparticles synthesized in a low-pressure plasma reactor containing argon and hydrogen. Nanoparticle sizes inferred from the TiRe-LII data agree with the results of a Brunauer-Emmett-Teller analysis.

Sipkens, T. A.; Mansmann, R.; Daun, K. J.; Petermann, N.; Titantah, J. T.; Karttunen, M.; Wiggers, H.; Dreier, T.; Schulz, C.

2014-09-01

338

Controlling laser-induced jet formation for bioprinting mesenchymal stem cells with high viability and high resolution.  

PubMed

Laser-assisted bioprinting is a versatile, non-contact, nozzle-free printing technique which has demonstrated high potential for cell printing with high resolution. Improving cell viability requires determining printing conditions which minimize shear stress for cells within the jet and cell impact at droplet landing. In this context, this study deals with laser-induced jet dynamics to determine conditions from which jets arise with minimum kinetic energies. The transition from a sub-threshold regime to jetting regime has been associated with a geometrical parameter (vertex angle) which can be harnessed to print mesenchymal stem cells with high viability using slow jet conditions. Finally, hydrodynamic jet stability is also studied for higher laser pulse energies which give rise to supersonic but turbulent jets. PMID:25215452

Ali, Muhammad; Pages, Emeline; Ducom, Alexandre; Fontaine, Aurelien; Guillemot, Fabien

2014-12-01

339

Screening and characterization of biopharmaceuticals by high-performance capillary electrophoresis with laser-induced native fluorescence detection.  

PubMed

High-performance capillary electrophoresis (HPCE) with laser-induced native fluorescence (LIF) detection is used to address significant problems in the quality control of biopharmaceuticals. All of the biopharmaceuticals studied can be detected at subnanomolar levels with linear dynamic ranges of at least 3 orders of magnitude. HPCE/LIF can determine impurities in "purified" biopharmaceuticals present in amounts less than 0.01% (i.e., at 4 x 10(-11) M) that of the major component. With HPCE/LIF, detection sensitivity is thus no longer a concern in the assaying of active ingredients in biopharmaceutical dosage formulations. The peptide mapping of biopharmaceuticals present at 1 x 10(-7) M (or an injected limit of detection of 60 amol) is presented. Also, kinetic information on the reaction of a recombinant enzyme-drug with its substrate present at the micromolar level has been extracted from electropherograms acquired in real-time. PMID:8354226

Lee, T T; Lillard, S J; Yeung, E S

1993-01-01

340

Morphological studies of laser-induced photoacoustic damage  

NASA Astrophysics Data System (ADS)

Argon-fluoride excimer laser ablation of stratum comeum causes deeper tissue damage than expected for thermal or photochemical mechanisms, suggesting thatphotoacoustic waves have arole in tissue damage. Laserirradiation (193 nm, 14 ns pulses, 1-2 Hz) attworadiantexposures, 60 and 160 mJ/cm2perpulse was usedto ablate the stratumcomeumofskin. Light and electron microscopy ofimmediate biopsies demonstrated damage to fibroblasts as deep as 88 and 220 jun, respectively, below the ablation site. Ablation throughwaterwas usedtoinertially confine the ablation zone. Partial ablationofs.c. through airproducedno damage, whereas partial ablation through water damaged skin to amean depth of 1 14.5 8.8( Full thickness ablation of s.c. through air and water produced damage zones measuring 192.2 16.2 and 293.0 71.6 rim, respectively (p <0.05). The increased depth ofdamage in the presence ofinertial confinementprovided by the layer of water strongly supports a photoacoustic mechanism ofdamage. The depths ofdamage for thelarge spot, line, and small spots were 43 1 164 urn, 269 96xni, andno damage. The spot size dependence ofthedepthofdamage is consistentwiththe geometric attenuation one would expect to be present from a pressure wave related phenomena. Sequential biopsies were taken over a 7 day period for light and transmission electron microscopy. At 24 hours, there was necrosis of the epidermis and papillary dermis subjacent to the ablation site, with neutrophils surrounding and demarcating the affected area. The necrotic zone sloughedby48 hours. Thereepithelializationwas completeby7 days. The sequenceofrepairis similartoknife wound healing which we have previously studied, and is analogous to other wound healing processes. We have used an experimental model of ArF excimer laser ablation of stratum corneum to investigate laser-induced photoacoustic damage. The evidence for the injury being due to pressure transients is indirectbutcompelling. Whether these pressuretransients are acoustic transients orshockwaves has notbeendetermined, although itis ourprejudicethatshockwaves are the predominant force under these conditions. It is important to consider the possible effects of pressure transients in evaluating laser-tissue interactions, particularly when using short pulse, high peak power lasers.

Flotte, Thomas J.; Yashima, Yutaka; Watanabe, Shinichi; McAuliffe, Daniel J., Sr.; Jacques, Steven L.

1990-06-01

341

Laser-Induced Breakdown Spectroscopy (LIBS) in Geochemical Analysis  

NASA Astrophysics Data System (ADS)

Laser-Induced Breakdown Spectroscopy (LIBS) analysis is being applied to an increasing number of geochemical problems, including mineral and rock analysis on the Mars rover Curiosity, elemental concentrations in ore minerals, identification of ore minerals, provenance determination of gems and other conflict minerals, geochemical mapping, correlation of rock units, and sample screening. LIBS is a laser ablation technique in which the photons emitted from electron transitions in the cooling plasma are diffracted and recorded as a spectrum. LIBS has several characteristics that set it apart from traditional, lab-based techniques. First, LIBS is relatively simple and requires no sample preparation, resulting in analysis that is portable, in situ, real-time, rapid, and inexpensive (in terms of equipment purchase, maintenance, and operating personnel). Second, each LIBS spectrum contains an enormous amount of information about the material. Most elements emit photons in the typical LIBS spectral range (200-1000 nm). Spectral interferences for which corrections are necessary in traditional techniques are additional, useful information in the LIBS spectrum, and recent work has demonstrated that some isotopic ratios can be measured with LIBS data. Thus, LIBS spectra are detailed chemical fingerprints of materials and the use of multivariate analysis can resolve issues that have been untouchable using traditional techniques. A good example is determination of country of origin for rubies and sapphires. Concentrations of key trace elements, as analyzed by LA-ICP-MS, have been used with marginal success to demonstrate that different deposits yield rubies or sapphires with unique, identifiable compositions. However, the fields for each deposit overlap in the 2- or 3-component diagrams commonly used. In contrast, it is possible to determine country of origin with greater than 90% accuracy using LIBS data, in which the intensities of 13,700 wavelengths are used as variables in multivariate analysis. Because LIBS spectra can accurately compare materials to each other, LIBS has great potential for rapid, field-based correlation, chemical mapping, and screening samples for further analysis. It also has potential for analytical situations in which we currently use high-precision data to ask the question "Are these materials the same or different?" For instance, trace element concentrations are used to identify sub-populations within detrital zircons of the same age. LIBS data may more easily distinguish such sub-populations.

McMillan, N. J.

2012-12-01

342

Laser damage thresholds in fused silica structured light gratings  

SciTech Connect

Computer-generated, ion-milled, holographic structures and gratings are being used for multiple splitting of high-power pulsed laser beams. The structures were manufactured by Teledyne Brown Engineering in Huntsville, Alabama, and both a linear grating and two dimensional structure were tested. Damage thresholds were measured in single-shot exposure using a 300mJ, 1{mu}m wavelength laser with a nominal 15ns gaussian pulse. Energy densities on the gratings were adjusted with a focusing lens and the energy distribution was mapped with an imaging profiler. The gratings were examined dynamically for sparking and breakdown. They were examined after exposure using phase contrast microscopy. Initial results indicate the grating surface is always damaged before the smooth surface independent of the beam direction. The initial indication is that the average energy density threshold for single-shot damage is in the excess of 12j/cm{sup 2}.

Frank, A.M.; Gillespie, C.H. [Lawrence Livermore National Lab., CA (United States)

1996-12-31

343

Fine phantom image from laser-induced proton radiography with a spatial resolution of several ?m  

NASA Astrophysics Data System (ADS)

The advantages of a laser-driven proton acceleration have prompted studies of laser-induced proton radiography. As the CR-39 solid-state nuclear-track detector is suitable for measuring charged particles and can be used in proton radiography, we studied laser-induced proton radiography with the CR-39 for several years, and we were able to obtain a spatial resolution of about 10 ?m. For obtaining an image with a spatial resolution of a few ?m, we investigated the effect of the CR-39 etching conditions on the spatial resolution and carried out imaging experiments using fine phantoms. Experiments were performed using the 100-TW titanium-sapphire laser system at the Advanced Photonics Research Institute of the Gwangju Institute of Science Technology. We have demonstrated that images with a spatial resolution of about several ?m can be achieved using laser-induced proton radiography.

Son, Jaebum; Lee, Cheol Ho; Kang, Jeongsoo; Jang, Doh-Yun; Park, Junesic; Kim, Yun Ho; Kim, Yong Kyun; Choi, Chang Il; Kim, I. Jong; Choi, Il Woo; Sung, Jae Hee; Lee, Seong Ku; Jeong, Tae Moon; Lee, Chang-Lyoul; Yu, Tae Jun; Lee, Jongmin

2014-07-01

344

Laser-induced breakdown spectroscopy detection of heavy metal in water based on graphite conch method  

NASA Astrophysics Data System (ADS)

The laser-induced breakdown spectroscopy emission characteristics of trace heavy metal lead in water is studied based on graphite conch method, with a 1064nm wavelength Nd: YAG laser as excitation source, the echelle spectrometer and ICCD detector are used for spectral separation and high sensitive detection with high resolution and wide spectral range. The delay time 900ns and gate time 1600ns are determined in the experiment. The calibration curve of Pb is plotted based on the different concentration measurement results, and a limit of detection of 0.0138mg / L is obtained for Pb in water. Graphite conch method effectively overcomes the current problems on laser-induced breakdown spectroscopy detection of heavy metal in water. The detection limits and stability are improved. The reference data is provided for further study on the fast measurement of trace heavy metals in water by laser induced breakdown spectroscopy technique.

Wang, Chunlong; Liu, Jianguo; Zhao, Nanjing; Shi, Huan; Liu, Lituo; Ma, Mingjun; Zhang, Wei; Chen, Dong; Liu, Jing; Zhang, Yujun; Liu, Wenqing

2012-10-01

345

Photophysics of Laser Dye-Doped Polymer Membranes for Laser-Induced Fluorescence Photogrammetry  

NASA Technical Reports Server (NTRS)

Laser-induced fluorescence target generation in dye-doped polymer films has recently been introduced as a promising alternative to more traditional photogrammetric targeting techniques for surface profiling of highly transparent or reflective membrane structures. We investigate the photophysics of these dye-doped polymers to help determine their long-term durability and suitability for laser-induced fluorescence photogrammetric targeting. These investigations included experimental analysis of the fluorescence emission pattern, spectral content, temporal lifetime, linearity, and half-life. Results are presented that reveal an emission pattern wider than normal Lambertian diffuse surface scatter, a fluorescence time constant of 6.6 ns, a pump saturation level of approximately 20 micro J/mm(exp 2), and a useful lifetime of more than 300,000 measurements. Furthermore, two demonstrations of photogrammetric measurements by laser-induced fluorescence targeting are presented, showing agreement between photogrammetric and physically measured dimensions within the measurement scatter of 100 micron.

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

2004-01-01

346

Detection of broadband terahertz waves with a laser-induced plasma in gases.  

PubMed

We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases. PMID:17025819

Dai, Jianming; Xie, Xu; Zhang, X-C

2006-09-01

347

Single-Walled Carbon Nanotubes, Carbon Nanofibers and Laser-Induced Incandescence  

NASA Technical Reports Server (NTRS)

Laser induced incandescence applied to a heterogeneous, multi-element reacting flows is characterized by a) temporally resolved emission spectra, time-resolved emission at selected detection wavelengths and fluence dependence. Laser fluences above 0.6 Joules per square centimeter at 1064 nm initiate laser-induced vaporization, yielding a lower incandescence intensity, as found through fluence dependence measurements. Spectrally derived temperatures show that values of excitation laser fluence beyond this value lead to a super-heated plasma, well above the vaporization of temperature of carbon. The temporal evolution of the emission signal at these fluences is consistent with plasma dissipation processes, not incandescence from solid-like structures.

Schubert, Kathy (Technical Monitor); VanderWal, Randy L.; Ticich, Thomas M.; Berger, Gordon M.; Patel, Premal D.

2004-01-01

348

Optimally enhanced optical emission in laser-induced air plasma by femtosecond double-pulse  

SciTech Connect

In laser-induced breakdown spectroscopy, a femtosecond double-pulse laser was used to induce air plasma. The plasma spectroscopy was observed to lead to significant increase of the intensity and reproducibility of the optical emission signal compared to femtosecond single-pulse laser. In particular, the optical emission intensity can be optimized by adjusting the delay time of femtosecond double-pulse. An appropriate pulse-to-pulse delay was selected, that was typically about 50 ps. This effect can be especially advantageous in the context of femtosecond laser-induced breakdown spectroscopy, plasma channel, and so on.

Chen, Anmin [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China) [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130012 (China); Li, Suyu; Li, Shuchang; Jiang, Yuanfei; Ding, Dajun [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China)] [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); Shao, Junfeng; Wang, Tingfeng [State Key Laboratory of Laser Interaction with Matter, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China)] [State Key Laboratory of Laser Interaction with Matter, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China); Huang, Xuri [Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130012 (China)] [Institute of Theoretical Chemistry, State Key Laboratory of Theoretical and Computational Chemistry, Jilin University, Changchun 130012 (China); Jin, Mingxing [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China) [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China); State Key Laboratory of Laser Interaction with Matter, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China)

2013-10-15

349

Online compositional analysis in coal gasification environment using laser-induced plasma technology  

NASA Astrophysics Data System (ADS)

Integrated Gasification Combined Cycle (IGCC) power plants have great potential for future clean-coal power generation. Today, the quality of coal is measured by sampling coal using various offline methods, and the syn-gas composition is determined by taking samples downstream of the gasifier and measured by gas chromatograph (GC). Laser induced plasma technology has demonstrated high sensitivity for elementary detection. The capability of free space transmission and focusing of laser beam makes laser induced plasma a unique technology for online compositional analysis in coal gasification environment and optimization control.

Deng, Kung-Li; Wu, Juntao; Wang, Zhe; Lee, Boon; Guida, Renato

2006-08-01

350

Detection of Broadband Terahertz Waves with a Laser-Induced Plasma in Gases  

SciTech Connect

We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases.

Dai Jianming; Xie Xu; Zhang, X.-C. [Center for Terahertz Research, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

2006-09-08

351

Laser induced damage thresholds and laser safety levels. Do the units of measurement matter?  

NASA Astrophysics Data System (ADS)

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 and to understand the correct scaling factors. This paper summarizes the theory and highlights the danger of using the wrong LIDT units in the context of potentially hazardous materials, laser safety eyewear and laser safety screens.

Wood, R. M.

1998-04-01

352

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

353

Circular Fibonacci gratings.  

PubMed

We introduce circular Fibonacci gratings (CFGs) that combine the concept of circular gratings and Fibonacci structures. Theoretical analysis shows that the diffraction pattern of CFGs is composed of fractal distributions of impulse rings. Numerical simulations are performed with two-dimensional fast Fourier transform to reveal the fractal behavior of the diffraction rings. Experimental results are also presented and agree well with the numerical results. The fractal nature of the diffraction field should be of great theoretical interest, and shows potential to be further developed into practical applications, such as in laser measurement with wideband illumination. PMID:22086040

Gao, Nan; Zhang, Yuchao; Xie, Changqing

2011-11-01

354

Mechanisms of Laser-Induced Dissection and Transport of Histologic Specimens  

PubMed Central

Rapid contact- and contamination-free procurement of histologic material for proteomic and genomic analysis can be achieved by laser microdissection of the sample of interest followed by laser-induced transport (laser pressure catapulting). The dynamics of laser microdissection and laser pressure catapulting of histologic samples of 80 ?m diameter was investigated by means of time-resolved photography. The working mechanism of microdissection was found to be plasma-mediated ablation initiated by linear absorption. Catapulting was driven by plasma formation when tightly focused pulses were used, and by photothermal ablation at the bottom of the sample when defocused pulses producing laser spot diameters larger than 35 ?m were used. With focused pulses, driving pressures of several hundred MPa accelerated the specimen to initial velocities of 100–300 m/s before they were rapidly slowed down by air friction. When the laser spot was increased to a size comparable to or larger than the sample diameter, both driving pressure and flight velocity decreased considerably. Based on a characterization of the thermal and optical properties of the histologic specimens and supporting materials used, we calculated the evolution of the heat distribution in the sample. Selected catapulted samples were examined by scanning electron microscopy or analyzed by real-time reverse-transcriptase polymerase chain reaction. We found that catapulting of dissected samples results in little collateral damage when the laser pulses are either tightly focused or when the laser spot size is comparable to the specimen size. By contrast, moderate defocusing with spot sizes up to one-third of the specimen diameter may involve significant heat and ultraviolet exposure. Potential side effects are maximal when samples are catapulted directly from a glass slide without a supporting polymer foil. PMID:17766336

Vogel, Alfred; Lorenz, Kathrin; Horneffer, Verena; Hüttmann, Gereon; von Smolinski, Dorthe; Gebert, Andreas

2007-01-01

355

Laser-induced acoustic desorption coupled with a linear quadrupole ion trap mass spectrometer.  

PubMed

In recent years, laser-induced acoustic desorption (LIAD) coupled with a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer has been demonstrated to provide a valuable technique for the analysis of a wide variety of nonvolatile, thermally labile compounds, including analytes that could not previously be analyzed by mass spectrometry. Although FT-ICR instruments are very powerful, they are also large and expensive and, hence, mainly used as research instruments. In contrast, linear quadrupole ion trap (LQIT) mass spectrometers are common due to several qualities that make these instruments attractive for both academic and industrial settings, such as high sensitivity, large dynamic range, and experimental versatility. Further, the relatively small size of the instruments, comparatively low cost, and the lack of a magnetic field provide some distinct advantages over FT-ICR instruments. Hence, we have coupled the LIAD technique with a commercial LQIT, the Thermo Fischer Scientific LTQ mass spectrometer. The LQIT was modified for a LIAD probe by outfitting the removable back plate of the instrument with a 6 in. ConFlat flange (CFF) port, gate valve, and sample lock. Reagent ions were created using the LQIT's atmospheric pressure ionization source and trapped in the mass analyzer for up to 10 s to allow chemical ionization reactions with the neutral molecules desorbed via LIAD. These initial experiments focused on demonstrating the feasibility of performing LIAD in the LQIT. Hence, the results are compared to those obtained using an FT-ICR mass spectrometer. Despite the lower efficiency in the transfer of desorbed neutral molecules into the ion trap, and the smaller maximum number of available laser pulses, the intrinsically higher sensitivity of the LQIT resulted in a higher sensitivity relative to the FT-ICR. PMID:20000769

Habicht, Steven C; Amundson, Lucas M; Duan, Penggao; Vinueza, Nelson R; Kenttämaa, Hilkka I

2010-01-15

356

Simulation of nanosecond pulsed laser ablation of copper samples: A focus on laser induced plasma radiation  

SciTech Connect

A thermal model for nanosecond pulsed laser ablation of Cu in one dimension and in ambient gas, He at 1 atm, is proposed in which equations concerning heat conduction in the target and gas dynamics in the plume are solved. These equations are coupled to each other through the energy and mass balances at interface between the target and the vapor and also Knudsen layer conditions. By assumption of local thermal equilibrium, Saha-Eggert equations are used to investigate plasma formation. The shielding effect of the plasma, due to photoionization and inverse bremsstrahlung processes, is considered. Bremsstrahlung and blackbody radiation and spectral emissions of the plasma are also investigated. Spatial and temporal distribution of the target temperature, number densities of Cu and He, pressure and temperature of the plume, bremsstrahlung and blackbody radiation, and also spectral emissions of Cu at three wavelengths (510, 516, and 521 nm) are obtained. Results show that the spectral power of Cu lines has the same pattern as CuI relative intensities from National Institute of Standard and Technology. Investigation of spatially integrated bremsstrahlung and blackbody radiation, and also Cu spectral emissions indicates that although in early times the bremsstrahlung radiation dominates the two other radiations, the Copper spectral emission is the dominant radiation in later times. It should be mentioned that the blackbody radiation has the least values in both time intervals. The results can be used for prediction of the optimum time and position of the spectral line emission, which is applicable in some time resolved spectroscopic techniques such as laser induced breakdown spectroscopy. Furthermore, the results suggest that for distinguishing between the spectral emission and the bremsstrahlung radiation, a spatially resolved spectroscopy can be used instead of the time resolved one.

Aghaei, M.; Mehrabian, S.; Tavassoli, S. H. [Laser and Plasma Research Institute, Shahid Beheshti University, G. C., Evin, Tehran, 1983963113 (Iran, Islamic Republic of)

2008-09-01

357

Visualization of laser-induced liquid micro-jet disintegration by means of high-speed video stroboscopy  

Microsoft Academic Search

In the present paper we describe a novel approach to monitor and to investigate laser induced liquid water jet disintegration in air and in vacuum. The features of liquid beam disintegration in vacuum are of importance for pulsed laser induced liquid beam desorption mass spectrometry and micro-calorimetry. Due to the small liquid beam diameter of 12-15 µm, its high speed

Boleslaw Stasicki; Ales Charvat; Manfred Faubel; Bernd Abel

2005-01-01

358

An intensity modulation based high-speed and high-resolution long-period fiber grating sensor interrogating system  

Microsoft Academic Search

A fast responding interrogation system based on intensity modulation using fiber Bragg gratings (FBG) has been developed to interrogate long period fiber grating (LPFG) sensor. Temperature and dynamic strain monitoring using this system have been successfully demonstrated. The performance of long period fiber grating (LPFG) sensors written in single cladding (SC) and double cladding (DC) fibers have been compared. This

Chia-Chin Chiang; Chow-Shing Shin; Shien-Kuei Liaw

2006-01-01

359

Bragg grating rogue wave  

E-print Network

We derive the rogue wave solution of the classical massive Thirring model, that describes nonlinear optical pulse propagation in Bragg gratings. Combining electromagnetically induced transparency with Bragg scattering four-wave mixing, may lead to extreme waves at extremely low powers.

Degasperis, Antonio; Aceves, Alejandro B

2015-01-01

360

Sampled-grating DBR laser-based analog optical transmitters  

Microsoft Academic Search

Sampled-grating distributed Bragg grating (SGDBR) laser-based widely tunable optical transmitters are investigated for application in high-performance analog links. More than 45 nm tuning range, 40 dB sidemode suppression ratio, and peak relative intensity noise below -153 dB\\/Hz is measured. SGDBR lasers integrated with semiconductor optical amplifiers and electroabsorption modulators (EAMs) are characterized with spurious free dynamic range of 125-127 dB·Hz45\\/

L. A. Johansson; Y. A. Akulova; G. A. Fish; L. A. Coldren

2003-01-01

361

LASER-INDUCED BREAKDOWN SPECTROSCOPY: A NEW TOOL FOR PROCESS CONTROL  

Microsoft Academic Search

Many industrial activities require adequate and timely evaluation of material composition. Laser-induced breakdown spectroscopy (LIBS) has, in recent years, shown a great potential for rapid qualitative and quantitative chemical analysis of various materials. In this paper, we will illustrate the usefulness of the LIBS technique for elemental analysis at different scales: from depth profilometry of thin coatings and the micron-scale

M. Sabsabi; V. Detalle; J. M. Lucas

362

Laser-induced photodissociation of oxyhemoglobin: Optical method of elimination of hypoxia (oxygen deficiency in biotissue)  

NASA Astrophysics Data System (ADS)

We consider the effect of laser-induced in vivo photodissociation of blood oxyhemoglobin on gas exchange in biological tissues. An optical method of laser-induced oxygenation of biotissues is developed and proposed. We show that, in the region of the action of the laser radiation, the degree of oxygenation of a tissue increases. We experimentally confirm that the phenomenon of laser-induced in vivo photodissociation of oxyhemoglobin opens up a new possibility of controlling the local concentration of free molecular oxygen in tissues, eliminating tissue hypoxia, and stimulating aerobic metabolism of cells. We show that the efficiency of the proposed method of laser-induced oxygenation of biotissues proves to be comparable with the efficiency of the hyperbaric oxygenation, but has the advantage of the locality of the action. The proposed optical method of local oxygenation of biotissues will make it possible to eliminate the problem of hypoxia in cancerous tumor tissue and to considerably increase the efficiency of photodynamic, radiation, and chemotherapy in modern oncology.

Asimov, M. M.; Thanh, Nguyen Cong

2011-08-01

363

Pump probe imaging of nanosecond laser induced bubbles in agar gel  

E-print Network

. The melting point of agar gel is very close to the boiling point of water, and the point of cellular damage nonlinearly with applied laser energy. We think that these last two facts point to the role that laser of femtosecond laser-induced breakdown in water from femtoseconds to microseconds," Optics Express 3

Aguilar, Guillermo

364

Double pulse laser induced breakdown spectroscopy applied to natural and artificial materials from cultural heritages  

Microsoft Academic Search

The laser-induced breakdown spectroscopy (LIBS) is an applied physical technique that has shown in recent years its great potential for rapid qualitative analysis of materials. Thanks to the possibility to implement a portable instrument that perform LIBS analysis, this technique is revealed to be particularly useful for in situ analysis in the field of cultural heritages. The purpose of this

Maria Brai; Gaetano Gennaro; Tiziano Schillaci; Luigi Tranchina

2009-01-01

365

Remote Femtosecond Laser Induced Breakdown Spectroscopy (LIBS) in a Standoff Detection Regime  

E-print Network

, MD 21005 e Laser Remote Sensing Laboratory, FAMU, 2077 Paul Dirac Dr. Tallahassee, FL, USA 32310Remote Femtosecond Laser Induced Breakdown Spectroscopy (LIBS) in a Standoff Detection Regime C Land, Proc. of SPIE Vol. 6219, 62190B, (2006) · 0277-786X/06/$15 · doi: 10.1117/12.663821 Proc. of SPIE

Van Stryland, Eric

366

High-Energy Fragmentation in Nanophotonic Ion Production by Laser-Induced Silicon Microcolumn Arrays  

E-print Network

High-Energy Fragmentation in Nanophotonic Ion Production by Laser-Induced Silicon Microcolumn. Although these surfaces are known to promote fragmentation of adsorbates at high laser fluences, the nature fragmentation methods, LISMA shows similarity to high-energy collision activated dissociation (CAD), ion

Vertes, Akos

367

Detection of fecal residue on poultry carcasses by laser induced fluorescence imaging techniques  

Technology Transfer Automated Retrieval System (TEKTRAN)

The potential use of laser-induced fluorescence imaging techniques was investigated for the detection of diluted fecal matters from various parts of the digestive tract, including colon, ceca, small intestine, and duodenum, on poultry carcasses. One of the challenges for using fluorescence imaging f...

368

High-Resolution Laser-Induced Breakdown Spectroscopy used in Homeland Security and Forensic Applications  

Microsoft Academic Search

The technique of laser-induced breakdown spectroscopy (LIBS) to detect elements for a variety of homeland security applications such as nuclear materials identification and inventory,and forensic applications has been demonstrated. For nuclear materials applications, we detected and profiled metals in coatings that were used to encapsulate nuclear fuel. Multivariate analysis has been successfully employed in the quantification of elements present in

Madhavi Z Martin; Stan D Wullschleger; Arpad Alexander Vass; Rodger Carl Martin; Henri Grissino-Mayer

2006-01-01

369

High resolution applications of laser-induced breakdown spectroscopy for environmental and forensic applications  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) has been used in the elemental analysis for a variety of environmental samples and as a proof of concept for a host of forensic applications. In the first application, LIBS was used for the rapid detection of carbon from a number of different soil types. In this application, a major breakthrough was achieved by using a

Madhavi Z. Martin; Nicole Labbé; Nicolas O Andre; Ronny D Harris; Michael H Ebinger; Stan D. Wullschleger; Arpad Alexander Vass

2007-01-01

370

Monte Carlo simulation of laser induced chemical vapor deposition Yehuda Zeiri, Uzi Atzmony, and Joseph Bloch  

E-print Network

Monte Carlo simulation of laser induced chemical vapor deposition Yehuda Zeiri, Uzi Atzmony 21 September 1989; accepted for publication 30 November 1990) We have used a Monte Carlo method developed a Monte Carlo procedure which was used to simulate the LICVD process. The beam inten- sities used

Zeiri, Yehuda

371

Parametric Study of Pellets for Elemental Analysis with Laser-Induced Breakdown Spectroscopy  

Microsoft Academic Search

The effect of various parameters on the accuracy of the laser-induced breakdown spectroscopy (LIBS) data taken from pellet samples has been investigated. The dependence of the standard deviation of the LIBS data on the amount and nature of the binder used, pressure used to press the powder into a pellet, and the position of the focal spot on the pellet

Bansi Lal; Hongbo Zheng; Fang-Yu Yueh; Jagdish P. Singh

2004-01-01

372

MULTISPECTRAL LASER-INDUCED FLUORESCENCE IMAGING SYSTEM FOR LARGE BIOLOGICAL SAMPLES  

Technology Transfer Automated Retrieval System (TEKTRAN)

Presented is a detailed description of a common aperture, multispectral laser-induced fluorescence imaging system developed to allow detection of fecal matter on agricultural products. With an expanded, 355 nm, Nd:YAG laser beam as the excitation source, fluorescence emission images in the blue, gr...

373

Analysis of protein-based binding media found in paintings using laser induced fluorescence spectroscopy  

Microsoft Academic Search

Laser induced fluorescence (LIF) spectroscopy of intrinsic fluorophores from organic media found in paintings (casein, animal glue and egg proteins) provides novel non-invasive means of characterisation of general classes of media on the basis of fluorescence emission arising from the presence of certain amino acids and their degradation byproducts. Proteins from traditionally employed binding media include collagen, casein, albumin and

Austin Nevin; Sharon Cather; Demetrios Anglos; Costas Fotakis

2006-01-01

374

Detection of bacterial infection of agave plants by laser-induced fluorescence  

Microsoft Academic Search

Greenhouse-grown plants of Agave tequilana Weber var. azul were inoculated with Erwinia carotovora, the causal agent of stem soft rot. We investigated the laser-induced fluorescence (LIF) of agave plants to determine whether LIF can be used as a noninvasive sensing tool for pathological studies. The LIF technique was also investigated as a means of detecting the effect of the polyamine

Jesus Cervantes-Martinez; Ricardo Flores-Hernandez; Benjamin Rodriguez-Garay; Fernando Santacruz-Ruvalcaba

2002-01-01

375

Fiber optic laser-induced fluorescence excitation emission detector applied to flow injection analysis  

Microsoft Academic Search

A multi-channel fiber optic laser induced fluorescence (LIF) detection system has been developed for flow injection analysis (FIA). It has been applied to the detection of standard PAH mixtures and real world samples. The instrument uses a fiber optic array to deliver Raman shifter generated excitation beams (260 nm - 340 nm) to samples flowing in a fused silica capillary.

Sean J. Hart; Gregory J. Hall; Jonathan E. Kenny

1999-01-01

376

Study of the laser-induced forward transfer of liquids for laser bioprinting  

Microsoft Academic Search

Laser-induced forward transfer (LIFT) is a direct-writing technique that allows printing patterns of diverse materials with a high degree of spatial resolution. In conventional LIFT a small fraction of a solid thin film is vaporized by means of a laser pulse focused on the film through its transparent holder, and the resulting material recondenses on the receptor substrate. It has

M. Duocastella; M. Colina; J. M. Fernández-Pradas; P. Serra; J. L. Morenza

2007-01-01

377

Recognition of edible oil by using BP neural network and laser induced fluorescence spectrum  

NASA Astrophysics Data System (ADS)

In order to accomplish recognition of the different edible oil we set up a laser induced fluorescence spectrum system in the laboratory based on Laser induced fluorescence spectrum technology, and then collect the fluorescence spectrum of different edible oil by using that system. Based on this, we set up a fluorescence spectrum database of different cooking oil. It is clear that there are three main peak position of different edible oil from fluorescence spectrum chart. Although the peak positions of all cooking oil were almost the same, the relative intensity of different edible oils was totally different. So it could easily accomplish that oil recognition could take advantage of the difference of relative intensity. Feature invariants were extracted from the spectrum data, which were chosen from the fluorescence spectrum database randomly, before distinguishing different cooking oil. Then back propagation (BP) neural network was established and trained by the chosen data from the spectrum database. On that basis real experiment data was identified by BP neural network. It was found that the overall recognition rate could reach as high as 83.2%. Experiments showed that the laser induced fluorescence spectrum of different cooking oil was very different from each other, which could be used to accomplish the oil recognition. Laser induced fluorescence spectrum technology, combined BP neural network?was fast, high sensitivity, non-contact, and high recognition rate. It could become a new technique to accomplish the edible oil recognition and quality detection.

Mu, Tao-tao; Chen, Si-ying; Zhang, Yin-chao; Guo, Pan; Chen, He; Zhang, Hong-yan; Liu, Xiao-hua; Wang, Yuan; Bu, Zhi-chao

2013-09-01

378

Acetone: a tracer for concentration measurements in gaseous flows by planar laser-induced fluorescence  

Microsoft Academic Search

This paper explores the use of acetone as a suitable tracer in planar laser-induced fluorescence concentration measurements in gaseous flows. The photophysics and physical properties of acetone relevant to its use as a fluorescent marker are discussed and compared to those of alternative molecular tracers, particularly the biacetyl molecule. Finally, as a direct example, concentration images obtained in a turbulent

A. Lozano; B. Yip; R. K. Hanson

1992-01-01

379

Measurements and Modeling of Acetone Laser-Induced Fluorescence with Implications for Temperature-Imaging Diagnostics  

Microsoft Academic Search

Recent determinations of the temperature dependence of acetone fluorescence have permitted the ap- plication of acetone planar laser-induced fluorescence imaging, which was already popular for mapping concentration, to the measurement of temperature. With a view toward developing temperature- imaging diagnostics, we present atmospheric-pressure fluorescence and absorption results acquired with excitation at eight wavelengths across the absorption feature of acetone and

Mark C. Thurber; Brian J. Kirby; Martin Votsmeier; Ronald K. Hanson

1998-01-01

380

Laser-induced photoacoustic spectroscopy for the speciation of transuranic elements in natural aquatic systems  

Microsoft Academic Search

Laser-induced Photoacoustic Spectroscopy (LPAS) is a new elegant instrumentation for the chemical speciation of aquatic transuranium (TRU) ions in very dilute concentrations (> 10–8 mol L–1). The aim of this paper is to review the application of LPAS to the study of the chemical behaviour of TRU ions in natural aquatic systems, the knowledge of which has become increasingly in

Jae-Il Kim; Reinhard Stumpe; Reinhardt Klenze

381

Laser induced fluorescence of the ferroelectric plasma source assisted hollow anode discharge  

E-print Network

Laser induced fluorescence of the ferroelectric plasma source assisted hollow anode discharge V high-current 1 kA , hollow anode HA , low-pressure 10-4 Torr Ar gas discharge were studied using a time of the HA cavity occurs due to the expansion of the plasma flows generated by the FPSs with a gradual time

382

Polishing-induced contamination of fused silica optics and laser induced damage density at  

E-print Network

Polishing-induced contamination of fused silica optics and laser induced damage density at 351 nm J the effect of contamination induced by fabrication process on laser damage density of fused silica polished for the considered parts. ©2005 Optical Society of America OCIS codes: (220.5450) Polishing; (140.3330) Laser damage

Boyer, Edmond

383

Morphology of femtosecond laser-induced structural changes in bulk transparent materials  

E-print Network

of structural changes induced in bulk glass by tightly focused femtosecond laser pulses. We observe a transitionMorphology of femtosecond laser-induced structural changes in bulk transparent materials Chris B from small density variations in the material to void formation with increasing laser energy

Schaffer, Chris B.

384

Laser-induced periodic alignment of Ag nanoparticles in soda-lime glass  

E-print Network

Laser-induced periodic alignment of Ag nanoparticles in soda-lime glass François Goutaland,1* Jean-organized structure formation on the bottom of femtosecond laser ablation craters in glass," Appl. Phys., A Mater. Sci properties. Towards this way, we present here the periodic pattern of a glass surface with silver

Paris-Sud XI, Université de

385

Means and method for capillary zone electrophoresis with laser-induced indirect fluorescence detection  

DOEpatents

A means and method for capillary zone electrphoresis with laser-induced indirect fluorescence detection. A detector is positioned on the capillary tube of a capillary zone electrophoresis system. The detector includes a laser which generates a laser beam which is imposed upon a small portion of the capillary tube. Fluorescence of the elutant electromigrating through the capillary tube is indirectly detected and recorded.

Yeung, Edward S. (Ames, IA); Kuhr, Werner G. (Riverside, CA)

1996-02-20

386

Means and method for capillary zone electrophoresis with laser-induced indirect fluorescence detection  

DOEpatents

A means and method for capillary zone electrphoresis with laser-induced indirect fluorescence detection. A detector is positioned on the capillary tube of a capillary zone electrophoresis system. The detector includes a laser which generates a laser beam which is imposed upon a small portion of the capillary tube. Fluorescence of the elutant electromigrating through the capillary tube is indirectly detected and recorded.

Yeung, Edwards (Ames, IA); Kuhr, Werner G. (Riverside, CA)

1991-04-09

387

Laser-induced breakdown spectroscopy and Raman microscopy for analysis of pigments in polychromes  

Microsoft Academic Search

A polychrome from the Rococo period was analysed by use of two laser-based analytical techniques, laser-induced breakdown spectroscopy (LIBS) and Raman microscopy. The analysis, performed on a fragment of a gilded altarpiece from the church of Escatrón, Zaragoza, Spain, provided detailed spectral data that have been used for the identification of pigments. LIBS measurements yielded elemental analytical data that suggest

Marta Castillejo; Margarita Mart??n; Diego Silva; Theodosia Stratoudaki; Demetrios Anglos; Lucia Burgio; Robin J. H Clark

2000-01-01

388

Analysis of pigments in polychromes by use of laser induced breakdown spectroscopy and Raman microscopy  

Microsoft Academic Search

Two laser-based analytical techniques, Laser Induced Breakdown Spectroscopy (LIBS) and Raman microscopy, have been used for the identification of pigments on a polychrome from the Rococo period. Detailed spectral data are presented from analyses performed on a fragment of a gilded altarpiece from the church of Escatrón, Zaragoza, Spain. LIBS measurements yielded elemental analytical data which suggest the presence of

M. Castillejo; M Mart??n; D. Silva; T. Stratoudaki; D. Anglos; L. Burgio; R. J. H Clark

2000-01-01

389

DEVELOPMENT OF LASER-INDUCED FLUORESCENCE DIAGNOSTIC FOR THE PAUL TRAP SIMULATOR EXPERIMENT  

E-print Network

available, stable, broadband, high-power laser system in this red spectrum region. Ions excited fromDEVELOPMENT OF LASER-INDUCED FLUORESCENCE DIAGNOSTIC FOR THE PAUL TRAP SIMULATOR EXPERIMENT M measurement of the transverse ion density profile in the PTSX device, which is essential for the study of beam

Gilson, Erik

390

New method for measuring low NO concentrations using laser induced two photon ionization  

E-print Network

New method for measuring low NO concentrations using laser induced two photon ionization Shan to the ionization area, and D is the diameter of the nozzle orifice , laser power, and electron multiplier voltage- length region free from laser generated background noise, signal-limited SL measurement conditions

Lee, Shan-Hu

391

Combined laser induced ignition and plasma spectroscopy: Fundamentals and application to a hydrogen–air combustor  

Microsoft Academic Search

Combined Laser Induced Ignition and Plasma Spectroscopy (LI2PS) has the potential to give the exact local composition of a mixture at the ignition point and at the ignition time. However, as different laser energies are required to ignite a particular mixture as function of space, the typical approach using two power meters to calibrate the plasma spectroscopy measurement is not

L. Zimmer; K. Okai; Y. Kurosawa

2007-01-01

392

Analysis of laser-induced breakdown spectroscopy spectra: The case for extreme value statistics  

Microsoft Academic Search

In most instances, laser-induced breakdown spectroscopy (LIBS) spectra are obtained through analog accumulation of multiple shots in the spectrometer CCD. The average acquired in the CCD at a given wavelength is assumed to be a good representation of the population mean, which in turn is implicitly regarded to be the best estimator for the central value of the distribution of

Anna P. M. Michel; Alan D. Chave

2007-01-01

393

Femtosecond laser-induced cavitations in the lens of the human eye  

Microsoft Academic Search

Ultrafast femtosecond lasers are used increasingly for a wide range of medical purposes. The immediate tissue response to pulses above a certain threshold is optically or laser induced breakdown, which is often visible as gas-filled cavities that persist for some time. In the present study, we attempted to define the cavitation threshold in the human lens in vitro using multiphoton

Line Kessel; Jose Nymand; Michael Harbst; Mike van der Poel; Lars Eskildsen; Michael Larsen

2007-01-01

394

PAPER www.rsc.org/loc | Lab on a Chip Laser-induced cavitation based micropump  

E-print Network

of cavitation in microfluidics, for example in microfluidic phase- change heat-exchangers.6 Yet, in the authorsPAPER www.rsc.org/loc | Lab on a Chip Laser-induced cavitation based micropump Rory Dijkinka as versatile and robust pumping techniques. Here, we present a cavitation based technique, which is able

Ohl, Claus-Dieter

395

EFFECT OF LASER INDUCED CRYSTALLINITY MODIFICATION ON BIODEGRADATION PROFILE OF POLY(L-LACTIC ACID)  

E-print Network

of surface crystallinity may have potential to tailor the initial PLLA degradation ratEFFECT OF LASER INDUCED CRYSTALLINITY MODIFICATION ON BIODEGRADATION PROFILE OF POLY(L-LACTIC ACID prevents the embedded drugs from releasing at the designed rate in the early stage. PLLA degradation

Yao, Y. Lawrence

396

Femtosecond laser-induced ablation of graphite K. Sokolowski-Tinten1  

E-print Network

be explained by a thermal ablation model, which describes material removal as hydrodynamic expansionFemtosecond laser-induced ablation of graphite K. Sokolowski-Tinten1 , S. Kudryashov1 , V. Temnov1-laser ablation of graphite has been investigated experimentally and theoretically. The experimental observation

von der Linde, D.

397

Ultrafast laser-induced changes in optical properties of semiconductors  

SciTech Connect

We study the effect of laser radiation on optical properties of semiconductors of industrial interest. The material is pumped with a laser of chosen central frequency, for which the absorption is maximal, thus inducing electron dynamics, which modifies the optical properties. By using an improved theoretical model, we study ultrafast dynamic changes in the refraction index and reflectivity corresponding to a wide frequency-interval of probing radiation and identify that interval where these optical changes are most significant.

Chirila, C. C.; Lim, Freda C. H.; Gavaza, M. G. [Institute of High Performance Computing, 1 Fusionopolis Way, 16-16 Connexis, 138632 (Singapore)

2012-04-01

398

Electrically-programmable diffraction grating  

DOEpatents

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

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

1998-05-26

399

Dark current and light illumination effects on grating formation during periodic long-term operation in photorefractive polymers  

SciTech Connect

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. [Center for Emergent Matter Science (CEMS), RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Mamiya, J. [Chemical Resources Laboratory, Tokyo Institute of Technology, R1-12, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Kawamoto, M. [Center for Emergent Matter Science (CEMS), RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Nano Medical Engineering Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Sassa, T., E-mail: tsassa@riken.jp [Center for Emergent Matter Science (CEMS), RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Advanced Device Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)

2014-01-14

400

Chiral fiber gratings: perspectives and challenges for sensing applications  

NASA Astrophysics Data System (ADS)

Chiral fiber gratings are produced in a microforming process in which optical fibers with noncircular or nonconcentric cores are twisted as they pass though a miniature oven. Periodic glass structures as stable as the glass material itself are produced with helical pitch that ranges from under a micron to hundreds of microns. The geometry of the fiber cross section determines the symmetry of the resulting structure which in turn determines its polarization selectivity. Single helix structures are polarization insensitive while double helix gratings interact only with a single optical polarization. Both single and double helix gratings may act as a fiber long period grating, coupling the core and cladding modes. The coupling is manifested in a series of narrow dips in the transmission spectrum. The dip position is sensitive to fiber elongation, twist and temperature, and to the refractive index of the surrounding medium. The suitability of chiral gratings for sensing pressure, temperature and liquid levels is investigated. Polarization insensitive single helix silica glass gratings display excellent stability up to temperatures of 600°C, while a pressure sensor with dynamic range of nearly 40 dB is demonstrated in polarization selective double helix gratings.

Kopp, Victor I.; Churikov, Victor M.; Zhang, Guoyin; Singer, Jonathan; Draper, Christopher W.; Chao, Norman; Neugroschl, Daniel; Genack, Azriel Z.

2007-07-01

401

Aspheric concave grating spectrographs  

NASA Technical Reports Server (NTRS)

The design of aspheric concave gratings for high-resolution spectroscopes is examined theoretically, using the requirements of the proposed Far-UV Spectroscopic Explorer (effective area 100 sq cm and lambda/delta lambda = 30,000 in the 90-120-nm range) as a concrete example and taking the limitations of current fabrication technology (straight grooves only and maximum density 6000 lines/mm) into account. The total-path function derived by Namioka (1961) for an ellipsoidal grating is subjected to aberration analysis to obtain the optical surface best suited to the design requirements; expressions for corrections to the conventional stigmatic Rowland-circle mount are obtained and shown to produce significant performance improvements; and the design advantages of coma-corrected non-Rowland geometries are explored. Ray tracings and deviation contours are provided.

Cash, W. C., Jr.

1984-01-01

402

Charged particle accelerator grating  

DOEpatents

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

Palmer, R.B.

1985-09-09

403

The Cryogenic Grating Spectrometer  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

404

Diffraction Gratings WDM Components  

NASA Astrophysics Data System (ADS)

Diffraction grating WDM components have tremendous capability in number of channels (160 channel components and more with bi-directionality are commercially available and components with two times more channels have been demonstrated experimentally). They have a high free spectral range (typically 775 nm with gratings working in the first order). Small spacing such as 25 GHz is commercially available and 5 GHz feasibility has been demonstrated. Athermal glass components down to 25 GHz spacing are manufactured with uncontrolled drifts as low as 0.35 pm/°C using commonly available glasses. These solutions are based on the traditional and mature optics technology used to manufacture millions of diffractionlimited reliable optics at low cost. The unique three-dimensional nature of these components can be exploited for advanced features requested by network designers such as add/drops, crossconnects, and routing devices. Cyclic passive routers accurately matched to the ITU frequencies in DWDM or to ITU wavelengths in CWDM have been proposed for advanced networks. Diffraction grating components can be used for high quality bidirectional links. For mono-directional or bi-directional links they have virtually unlimited numbers of channels and provide the lowest crosstalk for the higher number of channels. For low cost mass production the problems of fibre handling, that are the same with any solution, remain to be solved.

Laude, Jean-Pierre

405

Elastic continuum analysis of the liquid crystal polarization grating  

Microsoft Academic Search

We apply elastic continuum theory to model critical parameters influencing the free-energy equilibrium configuration and the dynamic performance of a continuous and in-plane liquid crystal profile acting as a polarization grating. We present analytical expressions for the threshold voltage, critical thickness, and the dynamic switching times under strong anchoring conditions, negligible flow, and arbitrary splay, twist, and bend constants. We

Ravi K. Komanduri; Michael J. Escuti

2007-01-01

406

Grating geophone signal processing based on wavelet transform  

NASA Astrophysics Data System (ADS)

Grating digital geophone is designed based on grating measurement technique benefiting averaging-error effect and wide dynamic range to improve weak signal detected precision. This paper introduced the principle of grating digital geophone and its post signal processing system. The signal acquisition circuit use Atmega 32 chip as core part and display the waveform on the Labwindows through the RS232 data link. Wavelet transform is adopted this paper to filter the grating digital geophone' output signal since the signal is unstable. This data processing method is compared with the FIR filter that widespread use in current domestic. The result indicates that the wavelet algorithm has more advantages and the SNR of seismic signal improve obviously.

Li, Shuqing; Zhang, Huan; Tao, Zhifei

2008-12-01

407

Quantitative assessment of wound-healing process as a response to laser-induced micro-injuries  

NASA Astrophysics Data System (ADS)

Currently, most investigations of wound healing rely on invasive biopsy followed by histology and immunohistochemistry staining. There is a great need to develop non-invasive techniques for in vivo diagnostic, clinical and scientific evaluation. Here, we performed a comprehensive investigation on the dynamic wound healing process as a response to laser-induced microinjuries using non-invasive imaging techniques such as reflectance laser-scanning confocal microscopy and video microscopy. Eight healthy subjects ranging from Fitzpatrick skin type II-VI with age from 27 to 57 years were recruited. The volar forearm of each subject was treated with a laser device that generates an array of microbeams with an infrared wavelength. The microscopic changes of epidermal cells and collagen during the wound healing process were assessed non-invasively using confocal microscopy. We also developed a quantitative method to evaluate the dynamic wound healing process at the microscopic level in three areas of interest: (1) treated micro-wounding zone, (2) surrounding collateral damage zone and (3) normal area. The depth-dependent intensity profile derived from reflectance confocal microscope images clearly distinguishes the three areas of interest and quantitatively measures the cellular structure-associated changes. A progressive change in depth-dependent intensity profiles in subjects with different ages parallels the clinical observation of wound healing rate. The quantitative analysis developed in this study may find broad applications in assessing the skin response to treatment at a microscopic level.

Liu, Yang; Bargo, Paulo; Kollias, Nikiforos

2009-02-01

408

2-dimensional ion velocity distributions measured by laser-induced fluorescence above a radio-frequency biased silicon wafer  

SciTech Connect

The dynamics of ions traversing sheaths in low temperature plasmas are important to the formation of the ion energy distribution incident onto surfaces during microelectronics fabrication. Ion dynamics have been measured using laser-induced fluorescence (LIF) in the sheath above a 30 cm diameter, 2.2 MHz-biased silicon wafer in a commercial inductively coupled plasma processing reactor. The velocity distribution of argon ions was measured at thousands of positions above and radially along the surface of the wafer by utilizing a planar laser sheet from a pulsed, tunable dye laser. Velocities were measured both parallel and perpendicular to the wafer over an energy range of 0.4–600 eV. The resulting fluorescence was recorded using a fast CCD camera, which provided resolution of 0.4 mm in space and 30 ns in time. Data were taken at eight different phases during the 2.2 MHz cycle. The ion velocity distributions (IVDs) in the sheath were found to be spatially non-uniform near the edge of the wafer and phase-dependent as a function of height. Several cm above the wafer the IVD is Maxwellian and independent of phase. Experimental results were compared with simulations. The experimental time-averaged ion energy distribution function as a function of height compare favorably with results from the computer model.

Moore, Nathaniel B.; Gekelman, Walter; Pribyl, Patrick [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States)] [Department of Physics and Astronomy, University of California, Los Angeles, California 90095 (United States); Zhang, Yiting; Kushner, Mark J. [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109-2122 (United States)] [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109-2122 (United States)

2013-08-15

409

GRIS: The grating infrared spectrometer  

Microsoft Academic Search

The grating infrared spectrometer (GRIS) is an echelle grating, prism cross-dispersed, spectrometer designed for the 2.3-m Steward Observatory telescope. The cross-dispersed format utilizes a Near Infrared Camera and Multi-Object Spectrometer 3 (NICMOS 3) HgCdTe detector array for observations in the 0.86-2.5 micrometer spectral region. An echelle grating, ruled on both sides, provides resolutions of 3449 and 9439 per slit width,

Rodger I. Thompson; Harland W. Epps; Greg Winters; William Womack; Eric Mentzell

1994-01-01

410

Particle Generation by Pulsed Excimer Laser Ablation in Liquid: Hollow Structures and Laser-Induced Reactions  

NASA Astrophysics Data System (ADS)

Pulsed laser ablation of solid targets in liquid media is a powerful method to fabricate micro-/nanoparticles, which has attracted much interest in the past decade. It represents a combinatorial library of constituents and interactions, and one can explore disparate regions of parameter space with outcomes that are impossible to envision a priori. In this work, a pulsed excimer laser (wavelength 248 nm, pulse width 30 ns) has been used to ablate targets in liquid media with varying laser fluences, frequencies, ablation times and surfactants. It is observed that hollow particles could be fabricated by excimer laser ablation of Al, Pt, Zn, Mg, Ag, Si, TiO2, and Nb2O5 in water or aqueous solutions. The hollow particles, with sizes from tens of nanometers to micrometers, may have smooth and continuous shells or have morphologies demonstrating that they were assembled from nanoparticles. A new mechanism has been proposed to explain the formation of these novel particle geometries. They were formed on laser-produced bubbles through bubble interface pinning by laser-produced solid species. Considering the bubble dynamics, thermodynamic and kinetic requirements have been discussed in the mechanism that can explain some phenomena associated with the formation of hollow particles, especially (1) larger particles are more likely to be hollow particles; (2) Mg and Al targets have stronger tendency to generate hollow particles; and (3) the 248 nm excimer laser is more beneficial to fabricate hollow particles in water than other lasers with longer wavelengths. The work has also demonstrated the possiblities to fabricate novel nanostructures through laser-induced reactions. Zn(OH)2/dodecyl sulfate flower-like nanostructures, AgCl cubes, and Ag2O cubes, pyramids, triangular plates, pentagonal rods and bars have been obtained via reactions between laser-produced species with water, electrolyes, or surfactant molecules. The underlying mechanisms of forming these structures have been discussed. The experimental results and the associated mechanisms developed in my research, and described in this thesis, have enriched the current understanding of particle generation by pulsed laser ablation in liquid. In so doing, my research has expanded the mechanistic routes for novel, or designer, nanoparticle geometries. Within the combinatorial and non-equilibrium environment provided by the unique experimental arrangement, the basic laws of material science still apply. Understanding and utilizing the laws will help researchers to fabricate new nanostructures by this and other methods providing similar environment.

Yan, Zijie

2011-12-01

411

Time Resolved Emissions from a Laser Induced Arc  

NASA Astrophysics Data System (ADS)

A 100 fs Ti:Sapphire laser was used to induce and guide an electrical discharge between a Van de Graf generator and a ground sphere. The discharge dynamics were quantified using a streak camera. The discharge is typically intiated by streamers propagating at approximately 1light. The streamers are followed by a much brighter flash of light which appears simultaneously at all points along the discharge. In some cases, the streamers are absent and only the flash appears, which suggests that photoionization by the laser beam is directly and solely responsible for the appearance of a conducting path and the subsequent flow of current.

Gordon, Daniel; Ting, Antonio; Briscoe, Eldridge; Manka, Charles; Fernsler, Richard

2002-11-01

412

Dissociative recombination in ultraviolet filamentary plasma gratings.  

PubMed

We investigated collisions of nitrogen and argon gas mixture with energetic electrons accelerated by Bragg incident intense infrared femtosecond laser pulses in ultraviolet filamentary plasma gratings. Significant decrease of fluorescence spectra of argon atoms were observed when a small amount of nitrogen gas was mixed with argon gas that facilitated observable argon-nitrogen collisions. We experimentally measured the fluorescence emission from the argon and nitrogen gas mixture under different driving pulse energies, the fluorescence decay dynamics after the impact excitation, as well as the fluorescence intensity dependence on the nitrogen and argon pressures. The experimental measurements were based on the electron acceleration and its subsequent impact with the gas mixture in the filamentary plasma gratings, which was essential for the observation of the dominant dissociative recombination in the gas mixture. PMID:24921794

Zhou, Hui; Li, Wenxue; Wang, Di; Shi, Liping; Ding, Liang'en; Zeng, Heping

2014-05-01

413

Transcutaneous laser-induced interstitial thermotherapy of nodular goiter  

NASA Astrophysics Data System (ADS)

In the experiment on 41 dogs the possibilities of Nd:YAG (1064 nm) and diode lasers (805 nm) usage for thermotherapy of thyroid gland was grounded. We founded the regimes of laser irradiation causing local destruction of thyroid glands without damage of surrounding organs and tissues. An intratissue dynamic thermometry control in the thyroid and surrounding tissues and their histological analysis were used for determination of the operating mode. The thermometry was performed with the help of an original setup, specimens for the analysis were taken in the period from 1 - 3 to 130 days after the laser irradiation. The results of the experiments gave occasion to the use of intrathyroid local laser hyperthermia in the treatment of 15 patients with recurrent nodal and multinodal euthyroid goiter and 2 patients with inoperable (incurable) medullary thyroid cancer. The laser thermotherapy was fulfilled transcutaneously with ultrasonic control. No complications were registered during the irradiation and the nearest postoperative period. The dynamic ultrasonic examination of the patients carried out for 3 - 18 months showed a positive effect in all cases.

Privalov, Valeriy A.; Seliverstov, Oleg V.; Revel-Muroz, Jean A.; Lappa, Alexander V.; Giniatulin, Ravil U.

2000-05-01

414

Laser-induced plasma chemistry of the explosive RDX with various metallic nanoparticles.  

PubMed

The feasibility of exploiting plasma chemistry to study the chemical reactions between metallic nanoparticles and molecular explosives such as cyclotrimethylenetrinitramine (RDX) has been demonstrated. This method, based on laser-induced breakdown spectroscopy, involves the production of nanoparticles in a laser-induced plasma and the simultaneous observation of time-resolved atomic and molecular emission characteristic of the species involved in the intermediate chemical reactions of the nanoenergetic material in the plasma. Using this method, it has been confirmed that the presence of aluminum promotes the ejection process of carbon from the intermediate products of RDX. The time evolution of species formation, the effects of laser pulse energy, and the effects of trace metal content on the chemical reactions were also studied. PMID:22410910

Gottfried, Jennifer L

2012-03-01

415

Diagnosis of laser-induced relativistic plasma by positron imaging technique  

SciTech Connect

Energetic deuterons emitted from laser-induced relativistic plasma are measured with a spatial resolution using a plate activated by them. Laser pulses of 33 TW in peak power and 34 fs in duration generate a plasma on a solid target, which is a microporous polytetrafluoroethylene film loaded with deuterated polystyrene, to accelerate deuterons. The deuterons are incident on a melamine plate, causing nuclear reactions of {sup 12}C(d,n){sup 13}N and {sup 14}N(d,n){sup 15}O. The spatial distributions of {sup 13}N and {sup 15}O created in the plate are visualized by a diagnosis using two-dimensional positron-emission tomography. The obtained images are further converted to temperature distribution of the emitted deuterons. The results show that the temperature of deuterons varies depending on the direction of deuteron emission. The present study provides knowledge of thermal equilibrium in laser-induced relativistic plasma in an ultrashort period of time.

Fujimoto, Masatoshi; Matsukado, Koji; Takahashi, Hironori; Kawada, Yoichi; Ohsuka, Shinji; Aoshima, Shin-ichiro [Central Research Laboratory, Hamamatsu Photonics K.K., 5000 Hirakuchi, Hamakita, Hamamatsu City 434-8601 (Japan)

2008-12-22

416

Picosecond laser-induced breakdown at 5321 and 5347 A - Observation of frequency-dependent behavior  

NASA Technical Reports Server (NTRS)

A study is presented of picosecond laser-induced breakdown at 3547 and 5321 A of several materials. The thresholds obtained for breakdown at 5321 A are compared to previous results obtained at 1.064 microns using the same laser system. This comparison illustrates the transition of bulk laser-induced breakdown as it becomes increasingly frequency dependent. UV picosecond pulses are obtained by mixing 5321 A and 1.064 micron pulses in a KH2PO4 crystal. Upper and lower bounds on the 3547 A breakdown threshold are defined, although some effects of walk-off distortion and self-focusing are observed. The results are discussed with reference to models for the intrinsic processes involved in the breakdown, i.e., avalanche and multiphoton ionization.

Smith, W. L.; Bechtel, J. H.; Bloembergen, N.

1977-01-01

417

Detection of lanthanides and actinides in solutions based on laser-induced luminescence and chemiluminescence  

NASA Astrophysics Data System (ADS)

This work is devoted to applications of the time-resolved laser- induced luminescence spectroscopy and time-resolved laser-induced chemiluminescence spectroscopy for detection of lanthanides and actinides. The limit of detection (LOD) of some lanthanides and actinides in solutions by the time-resolved laser luminescence spectroscopy is up to 10-13 mole/liter. Unfortunately, Pu, Np, and some U compounds do not produce luminescence in solutions, but when excited by laser radiation, they can induce chemiluminescence. The characteristics of chemiluminescence induced by excited lanthanide and actinide complexes in solutions are considered. A key problem of chemiluminescence application for lanthanide and actinide detection in solutions is the increase of the detection selectivity. This problem can be solved by using the multistep schemes of chemiluminescence excitation. It is shown that the time-resolved luminescence laser spectroscopy and chemiluminescence laser spectroscopy can be successfully used for detection of lanthanides and actinides in solutions.

Izosimov, I. N.; Firsin, N. G.; Gorshkov, N. G.; Nekhoroshkov, S. N.

2014-06-01

418

Probe Beam Detection of Laser-Induced Breakdown for Measuring Solubility of Actinide Compounds  

NASA Astrophysics Data System (ADS)

A nondestructive laser-induced breakdown detection technique is developed, which entails measuring the deflection of a probe laser beam due to a shock wave generated by a laser-induced breakdown of colloidal nanoparticles in liquids. Comparing this optical method with a previously developed acoustic detection method using a piezoelectric transducer, it enables remote measurement and therefore facilitates the in situ measurement of samples in a radiation-shielded glove box. The probe beam detection of a shock wave shows a sufficiently high sensitivity for monitoring the initial colloid formation when the uranium ion concentration exceeds the solubility limit of uranium hydrolysis compounds at a certain pH. The mean solubility product log Ksp° = -23.23 ±0.04 at an ionic strength of zero determined in this work agrees well with the previously reported result, log Ksp° = -23.19 ±0.43, measured by a calorimetric experiment on UO3·2H2O(cr).

Cho, Hye-Ryun; Jung, Euo Chang; Jee, Kwang Yong

2008-05-01

419

Time-synchronized continuous wave laser-induced fluorescence on an oscillatory xenon discharge  

SciTech Connect

A novel approach to time-synchronizing laser-induced fluorescence measurements to an oscillating current in a 60 Hz xenon discharge lamp using a continuous wave laser is presented. A sample-hold circuit is implemented to separate out signals at different phases along a current cycle, and is followed by a lock-in amplifier to pull out the resulting time-synchronized fluorescence trace from the large background signal. The time evolution of lower state population is derived from the changes in intensity of the fluorescence excitation line shape resulting from laser-induced fluorescence measurements of the 6s{sup Prime }[1/2]{sub 1}{sup 0}-6p{sup Prime }[3/2]{sub 2} xenon atomic transition at {lambda}= 834.68 nm. Results show that the lower state population oscillates at twice the frequency of the discharge current, 120 Hz.

MacDonald, N. A.; Cappelli, M. A. [Stanford Plasma Physics Laboratory, Stanford University, Stanford, California 94305 (United States); Hargus, W. A. Jr. [Air Force Research Laboratory, Edwards AFB, California 93524 (United States)

2012-11-15

420

Femtosecond laser-induced nanostructure-covered large-scale waves on metals  

NASA Astrophysics Data System (ADS)

Through femtosecond (fs) laser pulse irradiation (pulse duration: 65 fs, central wavelength: 800 nm, and repetition rate: 250 Hz), we investigate the morphological evolution of fs laser-induced periodic surface structure on Au and Pt, called a nanostructure-covered large-scale wave (NC-LSW) with a period of tens of microns, densely covered by iterating stripe patterns of nanostructures and microstructures. We show that the surface morphology of NC-LSW crucially depends on the fluence of the laser, the number of irradiating pulses, and the incident beam angle. Our experimental observations allow us to establish a three-step model for the NC-LSW formation: the formation of laser-induced surface unevenness, inhomogeneous energy deposition due to the interference between the incident light and the scattered field, and nonuniform energy deposition due to shielding by the peaks of LSW.

Hwang, Taek Yong; Guo, Chunlei

2013-12-01

421

Impurity and laser-induced damage in the growth sectors of rapidly grown DKP crystals  

SciTech Connect

We report the experimental results of impurity contamination and laser-induced damage investigations on rapidly grown potassium dihydrogen phosphate (KDP) crystals. Using absorption spectroscopy and chemical analysis, we determined the impurity distribution in the different growing sectors of KDP single crystals. The level of impurity was dependent on starting materials and growth rate. We also studied influence of impurities on laser-induced damage in fast grown KDP. The laser damage threshold (LDT) in the impurity-rich prismatic sector is same as in the high purity pyramidal sector within experimental error. Meanwhile, the LDT at the boundary of the prismatic and pyramidal sectors is less than half of that in the bulk. Furthermore, we found that the thermal annealing of the crystal eliminated the weakness of this sector boundary and increased its LDT to the same level as in the bulk of the crystal. Result suggests that the laser damage occurred in the vicinity of a high; localized strain field.

Yan, M.; Torres, R.; Runkel, M.; Woods, B.; Hutcheon, I.; Zaitseva, N.; DeYoreo, J.

1997-02-13

422

Laser-induced fluorescence of formaldehyde in combustion using third harmonic Nd:YAG laser excitation.  

PubMed

Formaldehyde (CH2O) is an important intermediate species in combustion processes and it can through laser-induced fluorescence measurements be used for instantaneous flame front detection. The present study has focussed on the use of the third harmonic of a Nd:YAG laser at 355 nm as excitation wavelength for formaldehyde, and different dimethyl ether (C2H6O) flames were used as sources of formaldehyde in the experiments. The investigations included studies of the overlap between the laser profile and the absorption lines of formaldehyde, saturation effects and the potential occurrence of laser-induced photochemistry. The technique was applied for detection of formaldehyde in an internal combustion engine operated both as a spark ignition engine and as a homogenous charge compression ignition engine. PMID:14607232

Brackmann, Christian; Nygren, Jenny; Bai, Xiao; Li, Zhongshan; Bladh, Henrik; Axelsson, Boman; Denbratt, Ingemar; Koopmans, Lucien; Bengtsson, Per-Erik; Aldén, Marcus

2003-12-01

423

Mechanisms of two-color laser-induced field-free molecular orientation.  

PubMed

Two mechanisms of two-color (?+2?) laser-induced field-free molecular orientation, based on the hyperpolarizability and ionization depletion, are explored and compared. The CO molecule is used as a computational example. While the hyperpolarizability mechanism generates small amounts of orientation at intensities below the ionization threshold, ionization depletion quickly becomes the dominant mechanism as soon as ionizing intensities are reached. Only the ionization mechanism leads to substantial orientation (e.g., on the order of ?0.1). For intensities typical of laser-induced molecular alignment and orientation experiments, the two mechanisms lead to robust, characteristic timings of the field-free orientation wave-packet revivals relative to the alignment revivals and the revival time. The revival timings can be used to detect the active orientation mechanism experimentally. PMID:23005623

Spanner, Michael; Patchkovskii, Serguei; Frumker, Eugene; Corkum, Paul

2012-09-14

424

Preliminary Design of Laser - induced Breakd own Spectroscopy for Proto - MPEX  

SciTech Connect

Laser-induced breakdown spectroscopy (LIBS) is a technique for measuring surface matter composition. LIBS is performed by focusing laser radiation onto a target surface, ablating the surface, forming a plasma, and analyzing the light produced. LIBS surface analysis is a possible diagnostic for characterizing plasma-facing materials in ITER. Oak Ridge National Laboratory (ORNL) has enabled the initial installation of a laser-induced breakdown spectroscopy diagnostic on the prototype Material-Plasma Exposure eXperiment (Proto-MPEX), which strives to mimic the conditions found at the surface of the ITER divertor. This paper will discuss the LIBS implementation on Proto-MPEX, preliminary design of the fiber optic LIBS collection probe, and the expected results.

Shaw, Guinevere C [ORNL] [ORNL; Biewer, T.M. [Oak Ridge National Laboratory (ORNL)] [Oak Ridge National Laboratory (ORNL); Martin, Madhavi Z [ORNL] [ORNL; Martin, Rodger Carl [ORNL] [ORNL

2014-01-01

425

Effect of laser-induced photodissociation of oxyhemoglobin on biomedical processes  

NASA Astrophysics Data System (ADS)

In the present report we draw attention to the phenomenon of laser-induced photodissociation of oxyhemoglobin in cutaneous blood vessels as an important factor in biostimulating and therapeutic action of low energy laser radiation. Calculations of absorption efficiency of laser radiation both by oxyhemoglobin and carbon monoxide hemoglobin were carried out by a computer simulation using Kubelka-Munk model of tissue. It has been shown that the absorption of the oxyhemoglobin in the visible region corresponding to the Q-band of absorption spectra possesses a relatively high selectivity. The obtained results are discussed in terms of developing new methods for wound healing, as well as for carbon monoacid poisoning. Some aspects of the laser-induced photodissociation of oxyhemoglobin complexes are discussed in view of its practical use for developing new diagnostic methods. An attractive way to use this phenomenon is monitoring of local concentrations of oxygen by laser light irradiation.

Asimov, Mustafo M.; Asimov, Rustam M.; Mirshahi, M.; Gisbrecht, Alexander

2001-04-01

426

Ultraviolet femtosecond and nanosecond laser ablation of silicon: Ablation efficiency and laser-induced plasma expansion  

SciTech Connect

Femtosecond laser ablation of silicon in air was studied and compared with nanosecond laser ablation at ultraviolet wavelength (266 nm). Laser ablation efficiency was studied by measuring crater depth as a function of pulse number. For the same number of laser pulses, the fs-ablated crater was about two times deeper than the ns-crater. The temperature and electron number density of the pulsed laser-induced plasma were determined from spectroscopic measurements. The electron number density and temperature of fs-pulse plasmas decreased faster than ns-pulse plasmas due to different energy deposition mechanisms. Images of the laser-induced plasma were obtained with femtosecond time-resolved laser shadowgraph imaging. Plasma expansion in both the perpendicular and the lateral directions to the laser beam were compared for femtosecond and nanosecond laser ablation.

Zeng, Xianzhong; Mao, Xianglei; Greif, Ralph; Russo, Richard E.

2004-03-23

427

DETERMINATION OF ALIPHATIC AMINES IN WATER USING DERIVATIZATION WITH FLUORESCEIN ISOTHIOCYANATE AND CAPILLARY ELECTROPHORESIS/LASER-INDUCED FLUORESCENCE DETECTION.  

EPA Science Inventory

Detection-oriented derivatization of aliphatic amines and amine functional groups in coumpounds of environmental interest was studied using fluorescein isothiocyanate (FITC) with separation/determination by capillary electrophoresis/laser-induced fluorescence. Determinative level...

428

Non-Gated Laser Induced Breakdown Spectroscopy Provides a Powerful Segmentation Tool on Concomitant Treatment of Characteristic and Continuum Emission  

E-print Network

We demonstrate the application of non-gated laser induced breakdown spectroscopy (LIBS) for characterization and classification of organic materials with similar chemical composition. While use of such a system introduces ...

Myakalwar, Ashwin Kumar

429

Laser-Induced Forward Transfer-printing of pre-machined crystalline magneto-optic garnet discs  

E-print Network

Laser-Induced Forward Transfer-printing of pre-machined crystalline magneto-optic garnet discs-optic Yttrium Iron Garnet films. Debris-free circular micro-discs with smooth edges and surface uniformity have

Sóbester, András

430

Analysis of laser-induced fluorescence spectra of in vitro plant tissue cultures  

NASA Astrophysics Data System (ADS)

We demonstrate the effectiveness of laser-induced fluorescence (LIF) for monitoring the development and stress detection of in vitro tissue cultures in a nondestructive and noninvasive way. The changes in LIF spectra caused by the induction of organogenesis, the increase of the F690/F740 ratio as a result of the stress originated in the organogenic explants due to shoot emergence, and the relationship between fluorescence spectra and shoot development were detected by LIF through closed containers of Saintpaulia ionantha.

Muñoz-Muñoz, Ana Celia; Gutiérrez-Pulido, Humberto; Rodríguez-Domínguez, José Manuel; Gutiérrez-Mora, Antonia; Rodríguez-Garay, Benjamín; Cervantes-Martínez, Jesús

2007-04-01

431

Quantitative measurements in laser-induced plasmas using optical probing. Final report.  

SciTech Connect

Optical probing of laser induced plasmas can be used to quantitatively reconstruct electron number densities and magnetic fields. Numerical techniques for extracting quantitative information from the experimental data are described. A computer simulation of optical probing is used to determine the quantitative information that can be reasonably extracted from real experimental interferometric systems to reconstruct electron number density distributions. An example of a reconstructed interferogram shows a steepened electron distribution due to radiation pressure effects.

Sweeney, D. W.

1981-01-01

432

Prospects for laser-induced breakdown spectroscopy for biomedical applications: a review  

Microsoft Academic Search

We review the different spectroscopic techniques including the most recent laser-induced breakdown spectroscopy (LIBS) for\\u000a the characterization of materials in any phase (solid, liquid or gas) including biological materials. A brief history of the\\u000a laser and its application in bioscience is presented. The development of LIBS, its working principle and its instrumentation\\u000a (different parts of the experimental set up) are

Vivek Kumar Singh; Awadhesh Kumar Rai

2011-01-01

433

Two-dimensional soot-particle sizing by time-resolved laser-induced incandescence  

NASA Astrophysics Data System (ADS)

The evaluation of the temporal decay of the laser-induced incandescence (LII) signal from soot particles is introduced as a technique to obtain two-dimensional distributions of particle sizes and is applied to a laminar diffusion flame. This novel approach to soot sizing exhibits several theoretical and technical advantages compared with the established combination of elastic scattering and LII, especially as it yields absolute sizes of primary particles without requiring calibration.

Will, Stefan; Schraml, Stephan; Leipertz, Alfred

1995-11-01

434

Numerical investigation of nanoparticle-assisted laser-induced interstitial thermotherapy toward tumor and cancer treatments  

Microsoft Academic Search

In this work, we numerically investigated nanoparticle-assisted laser-induced interstitial thermotherapy for tumor\\/cancer\\u000a treatments. The goal of the study was to investigate the therapeutic effects of treatment conditions including laser wavelength,\\u000a power, exposure time, concentrations of tailored nanoparticles, and optical\\/thermal properties of the tissue that is under\\u000a treatment. It was found that using absorbing preferential nanoparticles as the photothermal agent weakens

Xiao Xu; Andrew Meade; Yildiz Bayazitoglu

2011-01-01

435

In situ analysis of steel under reduced ambient pressure by laser-induced breakdown spectroscopy  

Microsoft Academic Search

We report on rapid in-situ analysis of liquid and solid steel samples under reduced ambient pressure by laser-induced breakdown spectroscopy (LIBS) using a transportable system. LIBS denotes a technique where a pulsed laser beam is used to ablate small amounts of the target material. The characteristic optical emission line intensities of the excited species in the laser-generated plasma plume allow

Johannes Heitz; Johann Gruber; Nikita Arnold; Dieter Bäuerle; Norbert Ramaseder; Wilfried Meyer; Johann Hochörtler

2003-01-01

436

New energy levels of atomic niobium by laser induced fluorescence spectroscopy in the near infrared  

NASA Astrophysics Data System (ADS)

Laser-induced fluorescence spectroscopy was applied in order to find new energy levels of the niobium atom. A continuous wave tuneable titanium–sapphire laser in the wavelength range from 750 to 865 nm and a hollow-cathode lamp were used. We discovered four energy levels of even parity, three lying levels below 19 000 cm?1 and one at much higher energy. Additionally hyperfine structure data of six levels of odd parity were determined.

Öztürk, I. K.; Ba?ar, Gö; Er, A.; Güzelçimen, F.; Ba?ar, Gü; Kröger, S.

2015-01-01

437

Laser-induced interstitial thermotherapy in treatment of recurrent nodular goiter and thyroid cancer  

NASA Astrophysics Data System (ADS)

Laser-induced interstitial thermotherapy was performed in 29 patients with recurrent nodular and multinodular goiter, and in 3 patients with recurrent inoperable thyroid cancer. There were used transcutaneous puncture under ultrasonic control, diode lasers with wavelength 805, 980, and 1060 nm, quartz monofibers, special computerized thermometer with microthermocouples. Disappearance or significant reduction of nodes in the most goiter cases, and regress of tumor in the cancer cases were marked during observation period (0.5 - 2.5 years).

Seliverstov, Oleg V.; Privalov, Valeriy A.; Lappa, Alexander V.; Demidov, A. K.; Faizrakhmanov, Alexey B.; Yarovoy, Nicolay N.

2001-10-01

438

O2-I laser (Oxygen-iodine) mixing studies using LIF (Laser Induced Fluorescence)  

Microsoft Academic Search

Laser Induced Fluorescence (LIF) was incorporated to study the degree of mixing in two subsonic nozzle variations for the O2-I laser system. The studies were performed using a testbed version of COIL-IV, an O2-I laser. I2 was injected through the nozzles and excited with an Ar laser to produce fluorescence. The observed jet trajectories could then be compared to trajectories

Y. D. Jones; D. Plummer; L. D. Watkins; G. D. Hager

1987-01-01

439

Remote Detection of Explosives by Enhanced Pulsed Laser Photodissociation\\/Laser-Induced Fluorescence Method  

Microsoft Academic Search

A unique scheme for remote detection of explosives has been demonstrated. High detection sensitivity was achieved by an exclusive\\u000a combination of two processes: Explosive vapor detection by PLP\\/LIF (pulsed laser photodissociation\\/laser-induced fluorescence)\\u000a with vapor concentration enhancement by remote evaporation. The basic PLP\\/LIF method was demonstrated on TNT in the vapor\\u000a phase with a detection sensitivity higher than 1 ppb m.

Talya Arusi-Parpar; Izhak Levy

440

Laser-Induced Breakdown Spectroscopy for the Analysis of Cobalt–Chromium Orthopaedic Wear Debris Particles  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) is investigated for the quantitative analysis of individual cobalt-chromium wear par- ticles generated in vivo from human artié cial knee joints. As imple- mented, the LIBS technique provided a measurement of the abso- lute chromium and cobalt masses for individual wear particles, which enabled calculation of chromium-to-cobalt mass ratios and the equivalent spherical diameter on a

E. A. Mokhbat; D. W. Hahn

2002-01-01

441

Cryogenic Laser Induced Fluorescence Characterization of U(VI) in Hanford Vadose Zone Pore Waters  

Microsoft Academic Search

Ambient and liquid helium temperature laser-induced time-resolved uranyl fluorescence spectroscopy was applied to study the speciation of aqueous uranyl solutions containing carbonate and phosphate and two porewater samples obtained by ultra-centrifugation of U(VI)-contaminated sediments. The significantly enhanced fluorescence signal intensity and spectral resolution found at liquid helium temperature allowed, for the first time, direct fluorescence spectroscopic observation of the higher

Zheming Wang; John M. Zachara; Wassana Yantasee; Paul L. Gassman; Chongxuan Liu; Alan G. Joly

2004-01-01

442

Observations of HONO by laser-induced fluorescence at the South Pole during ANTCI 2003  

Microsoft Academic Search

Observations of nitrous acid (HONO) by laser-induced fluorescence (LIF) at the South Pole taken during the Antarctic Troposphere Chemistry Investigation (ANTCI), which took place over the time period of Nov. 15, 2003 to Jan. 4, 2004, are presented here. The median observed mixing ratio of HONO 10 m above the snow was 5.8 pptv (mean value 6.3 pptv) with a

W. Liao; A. T. Case; J. Mastromarino; D. Tan; J. E. Dibb

2006-01-01

443

Laser-induced acoustic point source for accurate impulse response measurements within the audible bandwidth.  

PubMed

Laser induced air breakdown is proposed as a sound source for accurate impulse response measurements. Within the audible bandwidth, the source is repeatable, broadband, and omnidirectional. The applicability of the source was evaluated by measuring the impulse response of a room. The proposed source provides a more accurate temporal and spatial representation of room reflections than conventional loudspeakers due to its omnidirectionality, negligible size and short pulse duration. PMID:24907837

Gómez Bolaños, Javier; Delikaris-Manias, Symeon; Pulkki, Ville; Eskelinen, Joona; Hæggström, Edward

2014-06-01

444

Simultaneous laser-induced fluorescence and Raman imaging inside a hydrogen engine.  

PubMed

We report on the simultaneous and two-dimensional measurement of laser-induced fluorescence (LIF) and Raman scattering (Ramanography) applied inside a hydrogen internal combustion (IC) engine. Two different LIF tracer molecules, triethylamine (TEA) and trimethylamine (TMA), were used for the LIF experiments. The LIF and Raman results were found to be in very good agreement. The simultaneous application of Ramanography and LIF imaging indicated that TMA is the more suitable LIF tracer molecule, compared to TEA. PMID:20011004

Engel, Sascha Ronald; Koch, Peter; Braeuer, Andreas; Leipertz, Alfred

2009-12-10

445

Applications of laser-induced breakdown spectroscopy for geochemical and environmental analysis: A comprehensive review  

NASA Astrophysics Data System (ADS)

Applications of laser-induced breakdown spectroscopy (LIBS) have been growing rapidly and continue to be extended to a broad range of materials. This paper reviews recent application of LIBS for the analysis of geological and environmental materials, here termed "GEOLIBS" . Following a summary of fundamentals of the LIBS analytical technique and its potential for chemical analysis in real time, the history of the application of LIBS to the analysis of natural fluids, minerals, rocks, soils, sediments, and other natural materials is described.

Harmon, Russell S.; Russo, Richard E.; Hark, Richard R.

2013-09-01

446

Development of Laser-Induced Capillary Wave Method for Viscosity Measurement Using Pulsed Carbon Dioxide Laser  

Microsoft Academic Search

A new experimental apparatus, based on the laser-induced capillary wave method involving the use of a pulsed carbon dioxide laser (wavelength 10.6 µm, pulse width 50 ns, power 65 mJ) as a heating source has been developed. Since the present technique is applicable to a wide range of viscosity, this method is applicable to the process in which the viscosity drastically changes within

T. Oba; Y. Kido; Y. Nagasaka

2004-01-01

447

Open-air laser-induced chemical vapor deposition of silicon carbide coatings  

Microsoft Academic Search

This study demonstrates the open-air deposition of amorphous hydrogenated silicon carbide (a-SiC:H) by laser-induced chemical vapor deposition (LCVD) using an enclosureless (open-air) reactor system. Films are deposited on fused quartz substrates using the precursor gas trimethylsilane (TrMS). Based on Auger electron spectroscopy (AES), Fourier transform infrared absorption spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), the film's chemical composition and microstructure

Christopher J. Jensen; Wilson K. S. Chiu

2006-01-01

448

Evidence of inverse bremsstrahlung in laser enhanced laser-induced plasma  

SciTech Connect

Plasmas created by a Nd:yttrium aluminum garnet laser show systematic changes in local electron temperature when bathed by a continuous wave laser of increasing irradiance. By monitoring the local electron density, the laser light absorption coefficient, and the signal to noise ratio in neutral emissions, we explain the changes in electron temperature and signal to noise to be a consequence of inverse bremsstrahlung in this new system of laser enhanced laser-induced plasmas.

Wiggins, D. L.; Raynor, C. T.; Johnson, J. A. III [Center for Plasma Science and Technology, Florida A and M University, Tallahassee, Florida 32310 (United States)

2010-10-15

449

Laser-induced degradation of the photoluminescence intensity of porous silicon  

Microsoft Academic Search

Transmission Fourier-transform infrared (FTIR) spectroscopy has been used to monitor laser-induced degradation of the photoluminescence\\u000a (PL) intensity of porous Si. It is observed that the release of hydrogen from silicon hydride surface species coincides with\\u000a a decrease in the PL intensity and oxidation of the porous Si. The as-anodized PL characteristics can be recovered, with a\\u000a slight blue shift, by

C. Tsai; K.-H. Li; J. C. Campbell; B. K. Hance; J. M. White

1992-01-01

450

Pigment identification in paintings employing laser induced breakdown spectroscopy and Raman microscopy  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) was used in combination with Raman microscopy, for the identification of pigments in different types of painted works of art. More specifically, a 19th century post-Byzantine icon from Greece and two miniature paintings from France were examined and detailed spectral data are presented which lead to the identification of the pigments used. LIBS measurements yielded information

L. Burgio; K. Melessanaki; M. Doulgeridis; R. J. H. Clark; D. Anglos

2001-01-01

451

Novel probe for laser-induced breakdown spectroscopy and Raman measurements using an imaging optical fiber  

Microsoft Academic Search

A fiber-optic probe designed for remote laser-induced breakdown spectroscopy (LIBS), Raman spectroscopy, and Raman imaging has been developed for the microanalysis of solid samples. The probe incorporates both single-strand optical fibers and an image guide and allows atomic emission and Raman analysis of any spot on a solid sample within a 5 mm diameter field of view. The real-time sample

Brian J. Marquardt; Dimitra N. Stratis; S. M. Angel; D. A. Cremers

1998-01-01

452

Laser-induced ignition using a conical cavity in CH 4–air mixtures  

Microsoft Academic Search

A method that confines all the available energy in the vicinity of the ignition point during a laser-induced ignition process is proposed. It utilizes multiple reflection by a conical cavity surface when a small-diameter laser beam is directed into the cavity. Shadowgraphs of the early stages of the combustion process for quiescent methane\\/air mixtures show a hot gas jet to

M. H. Morsy; Y. S. Ko; S. H. Chung

1999-01-01

453

X-ray laser-induced photoelectron spectroscopy for single-state measurements  

Microsoft Academic Search

We demonstrate single-shot x-ray laser-induced time-of-flight photoelectron spectroscopy on metal and semiconductor surfaces with picosecond time resolution. Our compact multipulse terawatt tabletop x-ray laser source provides the necessary high photon flux (>1012?pulse), monochromaticity, picosecond pulse duration, and coherence for probing ultrafast changes in the chemical and electronic structure of these materials. Static valence band and shallow core-level photoemission spectra are

A. J. Nelson; J. Dunn; T. van Buuren

2004-01-01

454

X-ray laser-induced photoelectron spectroscopy for single-state measurements  

Microsoft Academic Search

We demonstrate single-shot x-ray laser-induced time-of-flight photoelectron spectroscopy on metal and semiconductor surfaces with picosecond time resolution. Our compact multipulse terawatt tabletop x-ray laser source provides the necessary high photon flux (>1012\\/pulse), monochromaticity, picosecond pulse duration, and coherence for probing ultrafast changes in the chemical and electronic structure of these materials. Static valence band and shallow core-level photoemission spectra are

A. J. Nelson; J. Dunn; T. van Buuren; J. Hunter

2004-01-01

455

Bioaerosols laser-induced fluorescence provides specific robust signatures for standoff detection  

Microsoft Academic Search

One of today's primary security challenges is the emerging biological threat due to the increased accessibility to biological warfare technology and the limited efficiency of detection against such menace. At the end of the 90s, Defence R&D Canada developed a standoff bioaerosol sensor, SINBAHD, based on intensified range-gated spectrometric detection of Laser Induced Fluorescence (LIF) with an excitation at 351

Sylvie Buteau; Jean-Robert Simard; Bernard Déry; Gilles Roy; Pierre Lahaie; Pierre Mathieu; Jim Ho; John McFee

2006-01-01

456

Laser induced damage in zinc tris(thiourea) sulfate and bis(thiourea) cadmium chloride  

Microsoft Academic Search

Laser induced damage threshold values are reported for two metal-organic complex crystals, zinc tris(thiourea) sulfate, and bis(thiourea) cadmium chloride. These crystals have single shot and multiple shot damage thresholds which are the highest among the solution grown crystals. The damage morphology, obtained by irradiating with fluences close to the threshold, reflects the symmetry of the face of the test site.

V. Venkataramanan; C. K. Subramanian; H. L. Bhat

1995-01-01

457

Laser induced damage in zinc tris(thiourea) sulfate and bis(thiourea) cadmium chloride  

NASA Astrophysics Data System (ADS)

Laser induced damage threshold values are reported for two metal-organic complex crystals, zinc tris(thiourea) sulfate, and bis(thiourea) cadmium chloride. These crystals have single shot and multiple shot damage thresholds which are the highest among the solution grown crystals. The damage morphology, obtained by irradiating with fluences close to the threshold, reflects the symmetry of the face of the test site. At higher fluences the damage leads to stress-induced fracture or thermo-chemical degradation.

Venkataramanan, V.; Subramanian, C. K.; Bhat, H. L.

1995-06-01

458

Examination of laser-induced cell lysis by time resolved imaging  

Microsoft Academic Search

Highly focused laser microbeams are being used with increasing regularity for targeted cell lysis, cellular microsurgery and molecular delivery via transient cell membrane permeabilization. To examine the mechanisms of laser induced cell lysis, we performed time-resolved imaging of confluent PtK2 cell cultures following the delivery of a single 6 ns, 532 nm Nd:YAG laser pulse. The laser pulse energies employed

Kaustubh R. Rau; Arnold Guerra III; Alfred Vogel; Vasan Venugopalan

2004-01-01

459

Jet formation upon ultrafast laser induced breakdown in the vicinity of liquid-gas interface  

Microsoft Academic Search

We have studied the phenomenon of breakdown in liquids under the action of ultrashort (160 fs) laser pulses focused in the vicinity of a flat or curved liquid-gas interface. It is established that a slightly divergent jet containing micron-sized bubbles is formed in the liquid, which originates from the laser-induced breakdown zone and propagates inward the liquid along the normal

S. V. Oshemkov; L. P. Dvorkin; V. Yu. Dmitriev

2008-01-01

460

Laser-Induced Forward Transfer: A Laser-Based Technique for Biomolecules Printing  

Microsoft Academic Search

\\u000a The high focusing power of lasers makes them adequate for micropatterning applications. Laser-induced forward transfer (LIFT)\\u000a is a direct-writing technique allowing the deposition of tiny amounts of material from a donor thin film to a solid substrate\\u000a through the action of a pulsed laser beam. Although LIFT was originally developed to operate with solid films, it has been\\u000a demonstrated that

P. Serra; M. Duocastella; J. M. Fernández-Pradas; J. L. Morenza

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