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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

Laser-induced thermal dynamic gratings in three-layer structures: active and nonactive substrates  

NASA Astrophysics Data System (ADS)

Time evolution of the intensity of light diffracted by phase grating which is induced by thermal dynamic grating (TDG) in liquid film between glass or quartz substrates is studied theoretically and experimentally. Due to heat exchange at the film boundaries the thermal gratings are also formed in substrates. The diffraction intensity of substrates can be less or comparable to that of film (non-active and active substrates, respectively). The experimental results are in a good agreement with the theoretical calculations carried out for the case when the film thickness is less the TDG period. It is shown the essential influence of the film thickness and the active-substrates contribution on the evolution of the intensity of diffracted light.

Ivakin, E. V.; Makarova, Ludmila; Rubanov, Alexander S.; Filippov, Valery N.

1998-11-01

3

Phase-controlled, heterodyne laser-induced transient grating measurements of thermal transport properties in opaque material  

E-print Network

The methodology for a heterodyned laser-induced transient thermal grating technique for non-contact, non-destructive measurements of thermal transport in opaque material is presented. Phase-controlled heterodyne detection ...

Johnson, Jeremy A.

4

Measurement of gas jet flow velocities using laser-induced electrostrictive gratings  

Microsoft Academic Search

.   We used time-resolved light scattering of cw probe laser radiation from laser-induced electrostrictive gratings for the determination\\u000a of flow velocities in air at room temperature. Some possibilities of the technique have been experimentally demonstrated with\\u000a submerged planar air jets in atmosphere, both for accumulated and single-shot measurements. The range of investigated flow\\u000a velocities was 5–200 m\\/s. The method of data

D. N. Kozlov; B. Hemmerling; A. Stampanoni-Panariello

2000-01-01

5

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

6

Time resolved laser-induced plasma dynamics  

NASA Astrophysics Data System (ADS)

The structure and evolution of the laser-induced vapor plume and shockwave were measured from femtosecond time resolved shadowgraph images. By changing the wavelength of the probe beam (400 and 800 nm), differences in the opacity of the vapor plume were measured as a function of delay time from the ablation laser pulse. The evolution of the temperature and electron number density during and after the ablation laser pulse were determined and compared for ablation in argon and helium background gases. A laser supported detonation wave (LSD) observed for ablation in argon, blocks the incoming laser energy and generates a high-pressure region above the vapor plume.

Mao, Xianglei; Wen, Sy-bor; Russo, Richard E.

2007-05-01

7

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

8

Laser-induced grating spectroscopy of Cr 3+-doped Gd 3Ga 5O 12 and Gd 3Sc 2Ga 3O 12 crystals  

NASA Astrophysics Data System (ADS)

The absorption and fluorescence spectra and fluorescence lifetimes of Cr 3+ ions in two garnet hosts, Gd 3Ga 5O 12 and Gd 3Sc 2Ga 3O 12, were measured as a function of temperature. In addition, laser-induced grating measurements were made as a function of laser power and write beam crossing angle for various temperatures between 10 and 300 K. For short writing times, Cr 3+ population gratings are produced and the observed signal dynamics were used to determine the properties of exciton migration in these materials. The exciton diffusion coefficient for Gd 3Ga 5O 12:Cr 3+ was found to decrease as temperature is raised while in Gd 3Sc 2Ga 3O 12:Cr 3+ the diffusion coefficient increases. Contributions to the laser-induced gratings from absorption and dispersion changes were determined and this was used to provide information on radiationless decay and excited state absorption processes. The differences in the results obtained on these two materials are attributed to the spectral effects produced by the different crystal field splittings of the Cr 3+ energy levels. For long writing times, long-lived changes in the refractive index were also observed and attributed to optically induced color centers.

Suchocki, Andrzej; Powell, Richard C.

1988-12-01

9

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

10

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

NASA Astrophysics Data System (ADS)

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

2010-06-01

11

Optical-fiber-to-waveguide coupling using carbon-dioxide-laser-induced long-period fiber gratings.  

PubMed

Optical fibers are expected to play a role in chip-level and board-level optical interconnects because of limitations on the bandwidth and level of integration of electrical interconnects. Therefore, methods are needed to couple optical fibers directly to waveguides on chips and on boards. We demonstrate optical-fiber-to-waveguide coupling using carbon-dioxide laser-induced long-period fiber gratings (LPFGs). Such gratings can be written in standard fiber and offer wavelength multiplexing-demultiplexing performance. The coupler fabrication process and the characterization apparatus are presented. The operation and the wavelength response of a LPFG-based optical-fiber-to-waveguide directional coupler are demonstrated. PMID:16127916

Bachim, Brent L; Ogunsola, Oluwafemi O; Gaylord, Thomas K

2005-08-15

12

Imaging ultrafast molecular dynamics with laser-induced electron diffraction.  

PubMed

Establishing the structure of molecules and solids has always had an essential role in physics, chemistry and biology. The methods of choice are X-ray and electron diffraction, which are routinely used to determine atomic positions with sub-ångström spatial resolution. Although both methods are currently limited to probing dynamics on timescales longer than a picosecond, the recent development of femtosecond sources of X-ray pulses and electron beams suggests that they might soon be capable of taking ultrafast snapshots of biological molecules and condensed-phase systems undergoing structural changes. The past decade has also witnessed the emergence of an alternative imaging approach based on laser-ionized bursts of coherent electron wave packets that self-interrogate the parent molecular structure. Here we show that this phenomenon can indeed be exploited for laser-induced electron diffraction (LIED), to image molecular structures with sub-ångström precision and exposure times of a few femtoseconds. We apply the method to oxygen and nitrogen molecules, which on strong-field ionization at three mid-infrared wavelengths (1.7, 2.0 and 2.3??m) emit photoelectrons with a momentum distribution from which we extract diffraction patterns. The long wavelength is essential for achieving atomic-scale spatial resolution, and the wavelength variation is equivalent to taking snapshots at different times. We show that the method has the sensitivity to measure a 0.1?Å displacement in the oxygen bond length occurring in a time interval of ?5?fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution. PMID:22398558

Blaga, Cosmin I; Xu, Junliang; DiChiara, Anthony D; Sistrunk, Emily; Zhang, Kaikai; Agostini, Pierre; Miller, Terry A; DiMauro, Louis F; Lin, C D

2012-03-01

13

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/?ε 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

14

RESEARCH PAPER Time-resolved dynamics of laser-induced micro-jets  

E-print Network

RESEARCH PAPER Time-resolved dynamics of laser-induced micro-jets from thin liquid films Matthew S and thick polymer laser-absorbing layers on the flow actuation mechanism and resulting jet dynamics. Both, we observe a transition to an alternate mechanism for jet formation, which is driven by the rapid

Arnold, Craig B.

15

BRIEF REPORT Dynamics of ArF Excimer Laser-induced  

E-print Network

BRIEF REPORT Dynamics of ArF Excimer Laser-induced Cavitation Bubbles in Gel Surrounded by a Liquid Medium Daniel Palanker, PhD, Igor Turovets, PhD, and Aaron Lewis, PhD* Laser Center, Hadassah Medical to be the driving force of tissue cutting in 193 nm ArF excimer laser-based vitreoretinal microsurgery

Palanker, Daniel

16

Features of photoinduced dynamic gratings in semiconductors  

SciTech Connect

The problem of influence of the diffusion process of nonequilibrium carriers on the efficiency of the dynamic grating photoinduced in a semiconductor material is studied theoretically and experimentally. An analytic expression is derived, which allows one to estimate the outlooks for applications of different semiconductor materials as active media for writing dynamic gratings. (nonlinear optical phenomena)

Grigor'ev, A M [Laser Technology Center Inc., St. Petersburg (Russian Federation)

2008-07-31

17

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 transformations: Molecular dynamics study Zhibin Lin and Leonid V. Zhigilei* Department of Materials Science dynamics simulations of a 20 nm Au film irradiated with 200 fs laser pulses of different intensity

Zhigilei, Leonid V.

18

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

19

Laser-induced magnetization dynamics and reversal in ferrimagnetic alloys  

NASA Astrophysics Data System (ADS)

This review discusses the recent studies of magnetization dynamics and the role of angular momentum in thin films of ferrimagnetic rare-earth-transition metal (RE-TM) alloys, e.g. GdFeCo, where both magnetization and angular momenta are temperature dependent. It has been experimentally demonstrated that the magnetization can be manipulated and even reversed by a single 40 fs laser pulse, without any applied magnetic field. This switching is found to follow a novel reversal pathway, that is shown however to depend crucially on the net angular momentum, reflecting the balance of the two opposite sublattices. In particular, optical excitation of ferrimagnetic GdFeCo on a time scale pertinent to the characteristic time of the exchange interaction between the RE and TM spins, i.e. on the time scale of tens of femtoseconds, pushes the spin dynamics into a yet unexplored regime, where the two exchange-coupled magnetic sublattices demonstrate substantially different dynamics. As a result, the reversal of spins appears to proceed via a novel transient state characterized by a ferromagnetic alignment of the Gd and Fe magnetic moments, despite their ground-state antiferromagnetic coupling. Thus, optical manipulation of magnetic order by femtosecond laser pulses has developed into an exciting and still expanding research field that keeps being fueled by a continuous stream of new and sometimes counterintuitive results. Considering the progress in the development of plasmonic antennas and compact ultrafast lasers, optical control of magnetic order may also potentially revolutionize data storage and information processing technologies.

Kirilyuk, Andrei; Kimel, Alexey V.; Rasing, Theo

2013-02-01

20

Dynamics of laser induced micro bubble clusters on tissue phantoms  

NASA Astrophysics Data System (ADS)

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

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

2011-03-01

21

Dynamics of laser-induced transient micro bubble clusters  

NASA Astrophysics Data System (ADS)

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

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

2009-07-01

22

Laser-induced ultrafast spin dynamics in ErFeO3  

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

23

Dynamic sampling of laser-induced vapor plumes by mass spectrometry  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

24

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

25

Dynamic observation of laser-induced damage made inside of transparent materials  

NASA Astrophysics Data System (ADS)

When we focus high power laser pulses on a surface or inside of transparent materials, non-linear absorption of the laser radiation occurs and some laser-induced damages are introduced. This process is used in laser marking of transparent materials. We have made dynamical observations of the process by the stroboscopic imaging system which has a few nanoseconds time resolution. Output of fundamental radiation (1064nm) from a Q-switched Nd:YAG laser was focused at the surface or inside of PMMA and soda glass blocks. Second harmonic radiation (532nm) form the same laser was used as illuminating light and images were taken by a CCD camera with a band-pass filter of 532 nm. Series of images were taken at different intervals between fundamental and second harmonic light, which was controlled by optical delay line. In observation at longer intervals than 50ns, another laser was used as illuminating score. Non-linear absorption in PMMA occurs at several points simultaneously and propagation of shock waves started from these points is clearly observed. Non-linear absorptions in soda glass occurs from inside outward along the laser beam. Laser- induced damages (cracks) continue to develop until some hundreds milliseconds after laser pulse. Effects of pulse energy and roughness of the target surface were examined.

Ito, Yoshiro; Kiyoku, Satoshi; Ogura, Tsutomu; Mohri, Naotake

2002-02-01

26

Laser-induced breathing modes in metallic nanoparticles: A symmetric molecular dynamics study  

SciTech Connect

A highly efficient simulation method based on molecular dynamics and group theory is adopted to investigate the laser-induced breathing oscillation of gold and silver nanospheres. Nanoparticles with size ranging from 5.8 to 46.2 nm are discussed. The effect due to laser-induced heating is modeled by a symmetric sudden expansion of the nanospheres by increasing the interatomic distances. A long-range empirical potential model which is capable of describing the phonon dispersion curves of noble metals in the full frequency range is established. Group theory is fully exploited to increase the computation efficiency, and the oscillation behavior of nanospheres of over 3 x 10{sup 6} atoms can be simulated efficiently. Oscillation frequencies of nanospheres are obtained by calculating the Fourier transform of the velocity autocorrelation function. The breathing modes of nanospheres are identified as the excitation of A{sub 1g} modes with in-phase radial displacement of atoms in the nanospheres. The resulting oscillation spectra are in very good agreement with experimental data.

Ng, Ming-Yaw; Chang, Yia-Chung [Research Center for Applied Sciences, Academia Sinica, Nankang, Taipei 115-29, Taiwan (China)

2011-03-07

27

Laser-induced breathing modes in metallic nanoparticles: A symmetric molecular dynamics study  

NASA Astrophysics Data System (ADS)

A highly efficient simulation method based on molecular dynamics and group theory is adopted to investigate the laser-induced breathing oscillation of gold and silver nanospheres. Nanoparticles with size ranging from 5.8 to 46.2 nm are discussed. The effect due to laser-induced heating is modeled by a symmetric sudden expansion of the nanospheres by increasing the interatomic distances. A long-range empirical potential model which is capable of describing the phonon dispersion curves of noble metals in the full frequency range is established. Group theory is fully exploited to increase the computation efficiency, and the oscillation behavior of nanospheres of over 3 × 106 atoms can be simulated efficiently. Oscillation frequencies of nanospheres are obtained by calculating the Fourier transform of the velocity autocorrelation function. The breathing modes of nanospheres are identified as the excitation of A1g modes with in-phase radial displacement of atoms in the nanospheres. The resulting oscillation spectra are in very good agreement with experimental data.

Ng, Ming-Yaw; Chang, Yia-Chung

2011-03-01

28

Dynamics and threshold behavior in polymer fiber Bragg grating creation  

NASA Astrophysics Data System (ADS)

Photosensitivity has been observed and Bragg gratings have been created in various polymer optical fibres in recent years. Nevertheless the mechanisms of Bragg grating formation in polymer optical fibres are yet to be fully investigated and understood. We carried out experimental investigations on the dynamic growth of Bragg grating under various exposure conditions. For the first time, we observed clearly a threshold behaviour in the grating creation process. The threshold distinguishes two types of fibre gratings that have quite differently properties and performance.

Peng, Gang-Ding; Liu, Hui Yong; Chu, Pak Lim

2002-11-01

29

Dynamic model of thermal reaction of biological tissues to laser-induced fluorescence and photodynamic therapy.  

PubMed

The aim of this work was to evaluate the temperature fields and the dynamics of heat conduction into the skin tissue under several laser irradiation conditions with both a pulsed ultraviolet (UV) laser (?=337??nm) and a continuous-wave (cw) visible laser beam (?=632.8??nm) using Monte Carlo modeling. Finite-element methodology was used for heat transfer simulation. The analysis of the results showed that heat is not localized on the surface, but is collected inside the tissue in lower skin layers. The simulation was made with the pulsed UV laser beam (used as excitation source in laser-induced fluorescence) and the cw visible laser (used in photodynamic therapy treatments), in order to study the possible thermal effects. PMID:23839531

Seteikin, Alexey Yu; Krasnikov, Ilya V; Drakaki, Eleni; Makropoulou, Mersini

2013-07-01

30

OH formation dynamics in 193 nm photolysis of 2-methoxyethanol: A laser induced fluorescence study  

NASA Astrophysics Data System (ADS)

Dynamics of OH radical formation in the 193 nm photolysis of 2-methoxyethanol is studied using Laser Photolysis-Laser Induced Fluorescence technique. The nascent state distribution of the OH radical is measured. The OH fragments are formed vibrationally cold, characterized by a Boltzmann-like single rotational temperature of 450 ± 100 K. The spin-orbit and ?-doublet ratios of OH fragments are measured. The relative average translational energy of the OH channel is determined to be 17.0 ± 3.0 kcal/mol. The experimental studies along with theoretical calculations suggest a complex mechanism for OH formation consisting of at least three pathways. The prominent pathway at shorter timescale (<50 ns) involves crossing over to the nearby repulsive state, whereas, at longer timescale (>1 ms) involves a series of reaction with initial H3C-OCH2CH2OH bond cleavage, followed by rearrangement of OCH2CH2OH to CH2OCH2OH, and a final concerted step to generate OH and ethylene epoxide.

SenGupta, Sumana; Upadhyaya, Hari P.; Kumar, Awadhesh; Naik, Prakash D.

2014-10-01

31

Laser-Induced Forward Transfer Using Triazene Polymer Dynamic Releaser Layer  

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

32

Laser-Induced Forward Transfer Using Triazene Polymer Dynamic Releaser Layer  

SciTech Connect

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

Stewart, James Shaw [Empa Swiss Federal Laboratories for Materials Testing and Research, Ueberlandstrasse 129, 8600 Duebendorf (Switzerland); Paul Scherrer Institut, 5232 Villigen-PSI (Switzerland); Lippert, Thomas; Wokaun, Alexander [Paul Scherrer Institut, 5232 Villigen-PSI (Switzerland); Nagel, Matthias; Nueesch, Frank [Empa Swiss Federal Laboratories for Materials Testing and Research, Ueberlandstrasse 129, 8600 Duebendorf (Switzerland)

2010-10-08

33

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

E-print Network

is a complicated process, dependent on radiative, collision-based and evaporative cooling. To analyze the LII Professor of Mechanical Engineering Dept. of Mechanical and Nuclear Engineering, Penn State College of Engineering. Laser Induced Incandescence (LII) is a popular method to estimate the properties of soot

Bjørnstad, Ottar Nordal

34

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

PubMed Central

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

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

2012-01-01

35

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

36

Demodulation System for Fiber Optic Bragg Grating Dynamic Pressure Sensing  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

37

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

38

Fiber Bragg Grating Sensors for Dynamic Machining Applications  

Microsoft Academic Search

Fiber Bragg grating sensors have attracted considerable attention for measurement applications due to their greatly reduced size, low weight, and immunity to electromagnetic interference in comparison with traditional sensing methods. Dynamic measurement of industrial machine tools is useful for gauging surface accuracy, monitoring tool condition, and predicting process stability, but requires a robust sensing scheme. The small size and high

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

39

Fiber Bragg grating sensors for dynamic machining applications  

Microsoft Academic Search

Fiber Bragg grating sensors have attracted considerable attention for measurement applications due to their greatly reduced size, low weight, and immunity to electromagnetic interference in comparison with traditional sensing methods. Dynamic measurement of industrial machine tools is useful for gauging surface accuracy, monitoring tool condition, and predicting process stability, but requires a robust sensing scheme. The small size and high

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

2003-01-01

40

Transient Grating Measurements of Excitonic Dynamics in Single-Walled  

E-print Network

. Because of their small diameter (1 nm) and extended dimension along the tube axis, single-walled carbon nano- tubes (SWNTs) are characterized as quasi-one-dimensional charge carriers,1 with very lowTransient Grating Measurements of Excitonic Dynamics in Single-Walled Carbon Nanotubes: The Dark

Apkarian, V. Ara

41

Dynamics of charge clouds ejected from laser-induced warm dense gold nanofilms  

NASA Astrophysics Data System (ADS)

We report a systematic study of the ejected charge dynamics surrounding laser-produced 30-nm warm dense gold films using single-shot femtosecond electron shadow imaging and deflectometry. The results reveal a two-step dynamical process of the ejected electrons under high pump fluence conditions: an initial emission and accumulation of a large amount of electrons near the pumped surface region, followed by the formation of hemispherical clouds of electrons on both sides of the film, which escape into the vacuum at a nearly isotropic and constant velocity with an unusually high kinetic energy of more than 300 eV. We also developed a model of the escaping charge distribution that not only reproduces the main features of the observed charge expansion dynamics but also allows us to extract the number of ejected electrons remaining in the cloud.

Zhou, Jun; Correa, Alfredo A.; Li, Junjie; Tang, Shao; Ping, Yuan; Ogitsu, Tadashi; Li, Dong; Zhou, Qiong; Cao, Jianming

2014-10-01

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

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; Thevenaz, Luc

2013-01-01

44

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

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

45

Investigations of the ultrafast laser induced melt dynamics by means of transient quantitative phase microscopy (TQPm)  

NASA Astrophysics Data System (ADS)

Modifications of bulk aluminum irradiated well above ablation threshold (F < 300 J.cm-2) have been investigated in situ by means of shadowgraphy and transient quantitative phase microscopy (TQPm) using ultrafast laser radiation (tp=80 fs, ?=800 nm). This novel pump-probe technique enables quantitative time-resolved measurements of object's properties, e.g. dimensions of melt droplets and layer thickness or transient refractive index changes. A series of time-resolved phase images of vaporized material and/or melt, which are induced by n=1..8 pulses on an aluminum target, are obtained using TQPm. Dynamics and characteristics of melting, dependence of the ablated material volume on process parameters and thereby induced structural modifications have been studied. An increase of material ejection rate is observed at delay time of approximately ?=300 ns and ?>800 ns after the incident pulse. Transient refractive index modifications have been investigated in technical glass (Schott D263) by means of TQPm. By using high-repetition rate ultra-short pulsed laser radiation (tp=400 fs, ?=1045 nm, frep=1 MHz) focused by a microscope objective (w0 ~ 4 ?m) heat accumulation and thereby glass melting as well as welding is enabled. Transient optical phase variation has been measured up to ?=2.1 ?s after the incident pulse and can be attributed to the generation of free charge carriers and compression forces inside glass.

Mingareev, Ilya; Horn, Alexander

2008-05-01

46

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

PubMed

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

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

2013-07-01

47

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

48

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

49

A method for comparison of computational fluid dynamic simulation and planar laser induced fluorescence images for a supersonic flowfield  

NASA Astrophysics Data System (ADS)

Non-intrusive diagnostics, such as planar laser induced fluorescence (PLIF) provide an excellent means to interrogate flowfields with minimal perturbation to the thermodynamic state of the gas. In the case of PLIF, the diagnostic can provide multidimensional information regarding the spread of a tracer, such as I II, providing an excellent means for quantifying mixing between multiple streams of gases. The images obtained using PLIF can in turn be used to compare directly to images generated by computational fluid dynamic (CFD) simulations for the experiment, providing an excellent mechanism to compare CFD to experiment. An issue that exists with interpreting PLIF images from compressible flows is that the local density and temperature of the I II varies throughout the field of imaging, leading to variations in the rate of fluorescence and the rate of quenching of the excited state of I II. These variations lead to local changes in the number of photons generated during the course of the laser pulse that excites the I II, beyond the variation due to the varying density of I II. Thus, when comparing PLIF images for compressible flows with CFD simulation data, some effort should be made to ensure that the CFD image reflects the local variations in photon production that occur in compressible flows. A method is presented here where a CFD simulation data for a compressible PLIF experiment is used to predict the local photon production during the course of interrogating laser pulse. The experiment consists of a chemical oxygen-iodine laser mixing nozzle utilizing Mach 3 injection of a He/I II mixture into a Mach 2.5 crossflow with a mixture of He and O II and has strong compressibility. The method utilizes numerical solutions for the ordinary differential equations describing the state-to-state processes within the I II fluorescence process where I II(X) is pumped to the I II(B), fluoresces and is quenched. These equations are solved locally within the flowfield predicted by the CFD simulation to predict the variations within the photon production, and compare directly with PLIF images from the experiment.

Madden, Timothy J.; Noren, Carrie A.; Emmert, Luke; Heaven, Michael C.

2008-02-01

50

Slow dynamics in a semiconductor laser coupled to fiber Bragg grating  

Microsoft Academic Search

Dynamics of a semiconductor laser coupled to a fiber Bragg grating is analyzed thanks to a map, which indicates the existence of low frequency fluctuations when the reflectivity and the bandwidth of the Bragg grating are varied. The influence of these parameters is detailed and we show how the filter can be used to control the laser dynamics.

A. V. Naumenko; Natalia A. Loiko; Celine Guignard; Pascal Besnard

2004-01-01

51

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

PubMed Central

The dynamic range of capillary electrophoresis analysis is ultimately limited by molecular shot noise at low concentrations and by concentration-induced band broadening at high concentrations. We report a system that approaches these fundamental limits. A laser-induced fluorescence detector is reported that employs a cascade of four fiber-optic beam-splitters connected in series to generate a primary signal and four attenuated signals, each monitored by a single-photon counting avalanche photodiode. Appropriate scaling of the signals from the five photodiodes produces a linear optical calibration curve for 5-carboxyl-tetramethylrhodamine from the concentration detection limit of 1 pM to the upper limit of 1 mM. Mass detection limits are 120 yoctomoles (70 molecules) injected into the instrument. The very-wide dynamic range instrument was used to study the metabolic products of the fluorescently labeled glycosphingolipid GM1-TMR produced by single cells isolated from the rat cerebellum. PMID:21410138

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

2011-01-01

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

Higher-harmonics nonlinear model for dynamical holographic grating formation in absorbent photopolymers  

NASA Astrophysics Data System (ADS)

Effects of spatiotemporal transformation of grating shape at nonlinear holographic recording in absorbent photopolymer have been investigated. We present an analytical model of dynamics of (N+1) spatial harmonics of spatial grating profiles with taking into consideration both record mechanisms (polymerization and components diffusion), absorption, interference pattern contrast and optional photopolymerization nonlinearity. Also we take into consideration so called additional gratings (AG) formed as a result of two waves mixing. On the base of numerical simulation we examined an influence of the material and record parameters on 2D spatial profiles of gratings.

Sharangovich, Sergey N.; Dovolnov, Eugene A.

2006-05-01

54

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

SciTech Connect

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

Tong, W.

1997-10-08

55

DWDM of fiber Bragg grating sensors without sensor spectral dynamic range limitation using CDMA  

Microsoft Academic Search

We demonstrate dense-wavelength-division multiplexing (DWDM) of fiber Bragg grating sensors without sensor spectral dynamic range limitation by combining code-division and wavelength-division multiplexing schemes

K. P. Koo; A. B. Tveten; S. T. Vohra

1999-01-01

56

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

NASA Astrophysics Data System (ADS)

The ability to use fiber-delivered erbium-laser radiation for non-contact arthroscopic meniscectomy in a liquid environment was studied. The laser radiation is transmitted through a water-vapor channel created by the leading part of the laser pulse. The dynamics of the channel formation around a submerged fiber tip was investigated with time-resolved flash photography. Strong pressure transients with amplitudes up to a few hundreds of bars measured with a needle hydrophone were found to accompany the channel formation process. Additional pressure transients in the range of kbars were observed after the laser pulse associated with the collapse of the vapor channel. Transmission measurements revealed that the duration the laser-induced channel stays open, and therefore the energy transmittable through it, is substantially determined by the laser pulse duration. The optimum pulse duration was found to be in the range between 250 and 350 µS. This was confirmed by histological evaluations of the laser incisions in meniscus: Increasing the pulse duration from 300 to 800 µs leads to a decrease in the crater depth from 1600 to 300 µm. A comparison of the histological examination after laser treatment through air and through water gave information on the influence of the vapor channel on the ablation efficiency, the cutting quality and the induced thermal damage in the adjacent tissue. The study shows that the erbium laser combined with an adequate fiber delivery system represents an effective surgical instrument liable to become increasingly accepted in orthopedic surgery.

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

1994-12-01

57

Four-wave mixing analysis of Brillouin dynamic grating in a polarization-maintaining fiber: theory and experiment.  

PubMed

We investigate the Brillouin dynamic grating generation and detection process in polarization-maintaining fibers for the case of continuous wave operation both theoretically and experimentally. The four interacting light waves couple together through the material density variation due to stimulated Brillouin scattering. The four coupled equations describing this process are derived and solved analytically for two cases: moving fiber Bragg grating approximation and undepleted pump and probe waves approximation. We show that the conventional grating model oversimplifies the Brillouin dynamic grating generation and detection process, since it neglects the coupling between all the four waves, while the four-wave mixing model clearly demonstrates this coupling process and it is verified experimentally by measuring the reflection of the Brillouin dynamic grating. The trends of the theoretical calculation and experimental results agree well with each other confirming that the Brillouin dynamic grating generation and detection process is indeed a four-wave mixing process. PMID:21997088

Zhou, Da-Peng; Dong, Yongkang; Chen, Liang; Bao, Xiaoyi

2011-10-10

58

PHYSICAL REVIEW E 85, 016319 (2012) Dynamics of primary and secondary microbubbles created by laser-induced breakdown of an  

E-print Network

along an axis whose unique angle rotates over time. This is a result of vorticity along the jet towards for a range of studies including those in fluid mechanics, shock wave dynamics, biophysical processes and pressure increase within the plasma, thereby initiating its explosive expansion. When formed in a liquid

Chen, Zhongping

59

Dynamic coating for resolving rhodamine B adsorption to poly(dimethylsiloxane)\\/glass hybrid chip with laser-induced fluorescence detection  

Microsoft Academic Search

In this paper a method was described about dynamic coating for resolving rhodamine B (RB) adsorption on a hybrid poly(dimethylsiloxane) (PDMS)\\/glass chip. The results showed that when the non-ionic surfactant Triton X-100 was higher than 0.5% (v\\/v) into the phosphate buffer, the adsorption of RB appeared. Besides, some separation conditions for RB were investigated, including concentration of Triton X-100, concentration

Jianzhen Kang; Jilin Yan; Jifeng Liu; Haibo Qiu; Xue-Bo Yin; Xiurong Yang; Erkang Wang

2005-01-01

60

Adaptive Sagnac interferometer with dynamic population grating in saturable rare-earth-doped fiber.  

PubMed

Sagnac fiber interferometer with the dynamic population grating formed in the rare-earth doped fiber is proposed for homodyne adaptive detection of optical phase modulation. The configuration is shown to be a simple all-optical fiber sensor suitable for linear high sensitivity detection of mechanical vibrations, acoustic signals, thermo-optic effect etc. Theoretical consideration shows that the quadratic response of this interferometric configuration associated with the amplitude dynamic grating is observed in the reflected wave mainly, while the recorded phase grating results in the linear energy exchange between the transmitted and reflected from the Sagnac loop light waves. Experiments with the erbium- and ytterbium-doped fiber based adaptive Sagnac configurations (with the operation wavelengths 1485 and 1,064 nm respectively) of the fiber accelerometers confirmed these general conclusions and demonstrated sensitivity of the fiber based interferometric configurations (~3 10?? rad/Hz¹/²) governed basically by the noise of the utilized lasers. PMID:23481961

Rivera, Jorge López; Sánchez, Marcos Plata; Miridonov, Alexei; Stepanov, Serguei

2013-02-25

61

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 the trapped molecule in its electronic B 3 0u state in ice. Independent of the initial excitation energy

Apkarian, V. Ara

62

A linearity interrogation technique with enlarged dynamic range for fiber Bragg grating sensing  

Microsoft Academic Search

An exact linearity interrogation technique with enlarged dynamic range for fiber Bragg grating (FBG) sensor has been analyzed theoretically and demonstrated experimentally. The technique bases on two matched FBGs for receiving the reflected signal from the sensor FBG and two photodiodes (PDs) for collecting the reflected signal from the two receiver FBGs. The linear expression between the nature logarithm of

Yage Zhan; Muhuo Yu; Jincheng Pei; Xichun Yang; Shiqing Xiang

2010-01-01

63

Dynamic Temperature Compensating Interrogation Technique for Strain Sensors With Tilted Fiber Bragg Gratings  

Microsoft Academic Search

In this letter, we propose a novel method of edge filter linear demodulation using tilted fiber Bragg gratings (TFBGs) in a fiber sensor system. Based on the filter characteristics of TFBGs and the same temperature characteristics as the FBG, the strain sensor demodulation system with dynamic temperature compensation can be achieved. An experimental system is built up to achieve one

Yinping Miao; Bo Liu; Weihua Zhang; Bo Dong; Haibin Zhou; Qida Zhao

2008-01-01

64

Dynamic grating recording in lyotropic ionic smectics of metal alkanoates doped with electrochromic impurities  

Microsoft Academic Search

In this work, we investigated nonlinear-optical properties in lyotropic ionic liquid crystals (LILC) of potassium caprilate doped with electrochromic impurities (viologens). It is known that after applying a direct electric field to the LILC-viologen cells colouration of samples is observed [1]. Dynamic grating recording under the action of nanosecond pulse laser radiation was obtained for the coloured samples. We analyzed

A. B. Bordyuh; Yu. A. Garbovskiy; S. A. Bugaychuk; G. V. Klimusheva; T. A. Mirnaya; G. G. Yaremchuk; A. P. Polishchuk

2009-01-01

65

Laser-Induced Incandescence Calibration via Gravimetric Sampling  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

66

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

SciTech Connect

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

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

2009-10-31

67

Dynamic tracking down-conversion signal processing method based on reference signal for grating heterodyne interferometer  

NASA Astrophysics Data System (ADS)

Traditional displacement measurement systems by grating, which purely make use of fringe intensity to implement fringe count and subdivision, have rigid demands for signal quality and measurement condition, so they are not easy to realize measurement with nanometer precision. Displacement measurement with the dual-wavelength and single-grating design takes advantage of the single grating diffraction theory and the heterodyne interference theory, solving quite well the contradiction between large range and high precision in grating displacement measurement. To obtain nanometer resolution and nanometer precision, high-power subdivision of interference fringes must be realized accurately. A dynamic tracking down-conversion signal processing method based on the reference signal is proposed. Accordingly, a digital phase measurement module to realize high-power subdivision on field programmable gate array (FPGA) was designed, as well as a dynamic tracking down-conversion module using phase-locked loop (PLL). Experiments validated that a carrier signal after down-conversion can constantly maintain close to 100 kHz, and the phase-measurement resolution and phase precision are more than 0.05 and 0.2 deg, respectively. The displacement resolution and the displacement precision, corresponding to the phase results, are 0.139 and 0.556 nm, respectively.

Wang, Guochao; Yan, Shuhua; Zhou, Weihong; Gu, Chenhui

2012-08-01

68

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

Microsoft Academic Search

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

James D. Smith; Volker Sick

2007-01-01

69

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

70

Dynamic range enhancement in fiber Bragg grating sensors using a multimode laser diode  

Microsoft Academic Search

A signal processing scheme for fiber Bragg grating sensors based on the utilization of adjacent modes of a multimode laser diode light source is demonstrated which allows high sensitivity to be obtained over a large measurement range. For strain measurements, a range of 4800 ?ε is achieved with a resolution of 0.08 ?ε\\/Hz, yielding a dynamic range of 95 dB

P. J. Moreira; L. A. Ferreira; J. L. Santos; F. Farahi

1999-01-01

71

Laser-induced dispersion control.  

PubMed

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

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

2014-06-01

72

Kinetic Approach for Laser-Induced Plasmas  

SciTech Connect

Non-equilibrium distribution functions of electron gas and phonon gas excited with ultrashort intense laser pulses are calculated for laser-induced plasmas occurring in solids. The excitation during femtosecond irradiation and the subsequent thermalization of the free electrons, as well as the dynamics of phonons are described by kinetic equations. The microscopic collision processes, such as absorption by inverse bremsstrahlung, electron-electron collisions, and electron-phonon interactions are considered by complete Boltzmann collision integrals. We apply our kinetic approach for gold by taking s-band electron into account and compare it with the case of excitation of d-band electrons.

Omar, Banaz; Rethfeld, Baerbel [Technical University of Kaiserslautern, Department of Physics, Erwin Schroedinger Str. 46, D-67663 Kaiserslautern (Germany)

2008-10-22

73

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

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

74

Curing dynamics of photopolymers measured by single-shot heterodyne transient grating method.  

PubMed

The heterodyne transient grating (HD-TG) method was first applied to the curing dynamics measurement of photopolymers. The curing dynamics for various monomers including an initiator (2.5 vol%) was monitored optically via the refractive index change after a single UV pulse irradiation. We could obtain the polymerization time and the final change in the refractive index, and the parameters were correlated with the viscosity, molecular structure, and reaction sites. As the polymerization time was longer, the final refractive change was larger, and the polymerization time was explained in terms of the monomer properties. PMID:23574665

Arai, Mika; Fujii, Tomomi; Inoue, Hayato; Kuwahara, Shota; Katayama, Kenji

2013-01-01

75

Color dynamics of diffraction gratings: evaluation and applications in optical security.  

PubMed

We looked for design methodologies that cope with optical specifications described in terms of trajectories in the CIE (Commission Internationale de l'Eclairage) 1976 chromaticity diagram in the context of low-cost mass-reproduction processes that inevitably introduce changes in the design of a diffractive device for security applications. The mathematics of the design process can be strongly simplified if the theory of planar waveguides (in integrated optics) is used to estimate, with sufficient accuracy, the position of Wood singularities, responsible for the more-interesting visual features of a grating. We show how to use such a model to assess color dynamics variations that are due to production and to estimate domains within the space of grating parameters that enable both first- and second-level security features to be implemented simultaneously. All the results are compared with the values obtained by rigorous coupled-wave analysis. PMID:18324265

Pires, P; Rebordão, J M

1999-12-11

76

Color dynamics of diffraction gratings: evaluation and applications in optical security  

NASA Astrophysics Data System (ADS)

We looked for design methodologies that cope with optical specifications described in terms of trajectories in the CIE (Commission Internationale de l Eclairage) 1976 chromaticity diagram in the context of low-cost mass-reproduction processes that inevitably introduce changes in the design of a diffractive device for security applications. The mathematics of the design process can be strongly simplified if the theory of planar waveguides (in integrated optics) is used to estimate, with sufficient accuracy, the position of Wood singularities, responsible for the more-interesting visual features of a grating. We show how to use such a model to assess color dynamics variations that are due to production and to estimate domains within the space of grating parameters that enable both first- and second-level security features to be implemented simultaneously. All the results are compared with the values obtained by rigorous coupled-wave analysis.

Pires, Paulo; Rebordo, Jose Manuel

1999-12-01

77

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

NASA Astrophysics Data System (ADS)

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

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

1996-04-01

78

Dynamics of laser induced thermoelastic expansion of native and coagulated ex-vivo soft tissue samples and their optical and thermo-mechanical properties  

NASA Astrophysics Data System (ADS)

The interferometric measurement of laser induced thermoelastic expansion of tissue samples can be used to estimate their optical, thermal and mechanical properties. This method was used to assess the Gruneisen coefficient and optical attenuation depth for native and coagulated ex-vivo bovine liver and porcine kidney samples. The results demonstrate decreases of 54% and 60% in the optical attenuation depth in bovine liver and porcine kidney after coagulation, respectively. The Gruneisen coefficient of native porcine kidney was determined to be 58% smaller (p < 0.05) that native bovine liver. The measured Gruneisen coefficients for native and coagulated ex-vivo porcine kidney were 0.07 +/- 0.03 and 0.105 +/- 0.02, respectively, whereas the Gruneisen coefficients for native and coagulated liver were 0.126 +/- 0.036 and 0.127 +/- 0.04, respectively. Our measurements indicate significant inter sample variability due likely to inherent variations in tissue optical absorption and surface preparation.

Soroushian, Behrouz; Whelan, William M.; Kolios, Michael C.

2011-03-01

79

Dynamical studies of gratings formed in polymer-dispersed liquid crystal films doped with a guest-host dye  

PubMed

This study investigated the dynamic behavior of the first-order diffraction efficiency of gratings formed in polymer-dispersed liquid crystal (PDLC) films doped with a guest-host dye. PDLC films were fabricated using various LC-polymer mixing ratios, and written with various powers. Experimental results indicated that several peaks appeared in the curve of the first-order diffraction efficiency versus time. According to the light scattering study, we believe that the first peak was due to the superposition of density and absorption gratings. The density grating was associated with the spatially varied molecular weight of polymer molecules across the sample, and the absorption grating resulted from the spatially varied density of free electrons. The other peaks were caused by the superposition of the absorption and phase gratings. The phase grating was generated by the formation of a periodic structure of polymer-rich and LC-rich regions in the sample. This study also proposes a model to explain these experimental results. Moreover, the theory derived from this model correlates well with the experimental results, allowing us to determine the amplitude of the final grating. PMID:11088886

Fuh; Tsai; Lee; Fan

2000-09-01

80

Demodulation of fiber bragg grating sensors based on dynamic tuning of a multimode laser diode.  

PubMed

Dither demodulation of fiber Bragg grating sensors illuminated with multimode light from laser diodes is theoretically and experimentally investigated. Quasi-static temperature and strain sensitivities of 0.09 degrees C/ radical Hz and 0.6 microepsilon/ radical Hz are obtained. We show that it is possible to measure small ac signals that lie outside the feedback loop bandwidth by using a synchronous detection referenced to twice the dither frequency. In this situation, dynamic strain sensitivity of 3.3 n(epsilon)/ radical Hz is achieved. PMID:18323963

Ferreira, L A; Diatzikis, E V; Santos, J L; Farahi, F

1999-08-01

81

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

82

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

NASA Astrophysics Data System (ADS)

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

Dovgalenko, George E.; Wu, Ying

2009-05-01

83

High dynamic range temperature-compensated fibre Bragg gratings sensor for structural monitoring of buildings  

NASA Astrophysics Data System (ADS)

The distance changes between structural elements inside a building (e.g. walls, pillars, stairs, etc.) ought to be monitored, especially in seismic-prone areas, in order to assess its stability. Fibre Bragg grating (FBG) sensors are now the most interesting choice for this purpose, since several gratings can be included in the fibre, resulting in a quasi-distributed sensor, which can be illuminated using a single light source and interrogated simply by a single optical spectrum analyzer (OSA), using wavelength multiplexing. The paper deals with such a sensor, which was installed for monitoring the distance changes in a construction joint between two building blocks inside the University "Politehnica" of Bucharest. Since this city is placed in a seismic-prone area, we use a fast scanning OSA, so that the dynamic behavior of the monitored construction joint is expected to be captured during future earthquakes. Slow drifts of the construction joint width will be also monitored. The paper describes the sensor structure and working principle, the experimental tests and main parameters evaluation. The reported sensor is temperature compensated. It has an estimated distance resolution better or equal to 10 ?m, and a linearity of +0.2%...-0.35% for displacements up to 0.55 mm. Simulated dynamic tests are also reported.

Smeu, E.; Gnewuch, H.; Jackson, D. A.; Podoleanu, A.

2006-06-01

84

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

85

Laser-induced breakdown spectroscopy in China  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) has been regarded as a future superstar for chemical analysis for years due to its unique features such as little or no sample preparation, remote sensing, and fast and multi-element analysis. Chinese LIBS community is one of the most dynamically developing communities in the World. The aim of the work is to inspect what have been done in China for LIBS development and, based on the understanding of the overall status, to identify the challenges and opportunities for the future development. In this paper, the scientific contributions from Chinese LIBS community are reviewed for the following four aspects: fundamentals, instrumentation, data processing and modeling, and applications; and the driving force of LIBS development in China is analyzed, the critical issues for successful LIBS application are discussed, and in our opinion, the potential direction to improve the technology and to realize large scale commercialization in China is proposed.

Wang, Zhe; Yuan, Ting-Bi; Hou, Zong-Yu; Zhou, Wei-Dong; Lu, Ji-Dong; Ding, Hong-Bin; Zeng, Xiao-Yan

2014-08-01

86

Molecular dynamics of the interfacial properties of partially fluorinated polymer dispersed liquid crystal gratings  

NASA Astrophysics Data System (ADS)

The interfacial properties of polymer dispersed liquid crystal (PDLC) gratings influenced by partial matrix fluorination are studied through molecular dynamics methods. The miscibility between the fluorine-substituted monomer and other materials in the prepolymer mixture is evaluated by using the solubility parameters of molecules. The interfacial effect of different fluorination levels is analysed theoretically. The results indicate that most fluorine-substituted monomers are distributed on the interface between the monomer and the LC. The interaction energy on the interface decreases with increasing fluorination, which can improve the electro-optical tunable performance of such gratings. However, it should also be noted that excessive fluorination may lead to penetration of fluorine-substituted monomers into the LC medium. Such a result will block the normal diffusion of LC during the photo-initiated polymerization-induced phase separation process. Through calculation of the radial distribution function, a reasonable alignment structure for LCs near the interface is given. The calculation of the order parameter shows that fluorination causes disorder of their orientation.

Zheng, Zhigang; Ma, Ji; Liu, Yonggang; Xuan, Li

2008-12-01

87

Plasma-Particle Interactions in a Laser-Induced Plasma: Implications for Laser-Induced  

E-print Network

Plasma-Particle Interactions in a Laser-Induced Plasma: Implications for Laser-Induced Breakdown of Florida, Gainesville, Florida 32611-6300 The interaction between laser-induced plasmas and indi- vidual of tens of microseconds within plasmas formed by 300-mJ Nd: YAG laser pulses. Significant spatial

Hahn, David W.

88

Beam dynamics and wakefield simulations of the double grating accelerating structure  

SciTech Connect

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

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

2012-12-21

89

Beam dynamics and wakefield simulations of the double grating accelerating structure  

NASA Astrophysics Data System (ADS)

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

Najafabadi, B. Montazeri; Byer, R. L.; Ng, C. K.; England, R. J.; Peralta, E. A.; Soong, K.; Noble, R.; Wu, Z.

2012-12-01

90

Ultrafast laser-induced subwavelength structures towards nanoscale: the significant role of plasmonic effects  

E-print Network

Nowadays, aiming at manipulating light beyond diffraction limit, plasmonics based on elaborate artificialities benefiting from the advance of nano-manufacturing has aroused great interest. Here, we demonstrate ultrafast active plasmonic structures - ultrafast laser-induced deep-subwavelength gratings (DSGs) - spontaneously generated in virtue of plasmonic effects rather than human innovation. The evidence that DSGs can derive from grating splitting reveals the plasmonic essence of the phenomenon - the conversion of surface plasmon (SP) modes. More generally, the universal scaling-down of ultrafast laser-induced structures towards nanoscale originates in the physical regime for plasmonic interaction turning from optical regime to electrostatic regime - the quasistatic SPs, which would bring laser-solid-matter interaction far beyond diffraction limit and ultrafast, non-thermal ablation for extraordinary electrostatic enhancement. In short, the SP-related mechanisms that are high significant for clarifying the p...

Huang, Min; Zhao, Fuli; Xu, Zhizhan

2011-01-01

91

Explaining the paradoxical diversity of ultrafast laser-induced demagnetization.  

PubMed

Pulsed-laser-induced quenching of ferromagnetic order has intrigued researchers since pioneering works in the 1990s. It was reported that demagnetization in gadolinium proceeds within 100 ps, but three orders of magnitude faster in ferromagnetic transition metals such as nickel. Here we show that a model based on electron-phonon-mediated spin-flip scattering explains both timescales on equal footing. Our interpretation is supported by ab initio estimates of the spin-flip scattering probability, and experimental fluence dependencies are shown to agree perfectly with predictions. A phase diagram is constructed in which two classes of laser-induced magnetization dynamics can be distinguished, where the ratio of the Curie temperature to the atomic magnetic moment turns out to have a crucial role. We conclude that the ultrafast magnetization dynamics can be well described disregarding highly excited electronic states, merely considering the thermalized electron system. PMID:20010830

Koopmans, B; Malinowski, G; Dalla Longa, F; Steiauf, D; Fähnle, M; Roth, T; Cinchetti, M; Aeschlimann, M

2010-03-01

92

Dynamic fiber Bragg grating strain sensor using a wavelength-locked tunable fiber ring laser  

NASA Astrophysics Data System (ADS)

The interrogation systems based on fiber-optic sensors are very attractive for the practical applications in structural health monitoring owing to a number of advantages of optical fiber elements over their electronic counterparts. Among the fiber-optic sensors, the fiber Bragg gratings (FBGs) have their own unique features to be widely used for detection of acoustic emission. We have developed a dynamic strain sensing system by using a tunable single longitudinal mode Erbium-doped fiber ring laser to be locked to the middle-reflection wavelength of the FBG as the demodulation technique. A proportional-integral-derivative device continuously controls the laser wavelength that is kept at the FBG middle-reflection wavelength, thus stabilizing the operating point against quasi-static perturbation, while the high frequency dynamic strain shifts the FBG reflection profile. The reflected power varies in proportion to the applied strain which can be derived directly from AC photocurrent of the reflected signal. We have designed and assembled a fourchannel demodulator system for simultaneous high frequency dynamic strain sensing.

Zhu, Yinian; Krishnaswamy, Sridhar

2012-04-01

93

High pressure sensing and dynamics using high speed fiber Bragg grating interrogation systems  

NASA Astrophysics Data System (ADS)

Fiber Bragg gratings (FBGs) are developing into useful sensing tools for measuring high pressure dynamics in extreme environments under shock loading conditions. Approaches using traditional diode array coupled FBG interrogation systems are often limited to readout speeds in the sub-MHz range. For shock wave physics, required detection speeds approaching 100 MHz are desired. We explore the use of two types of FBG sensing systems that are aimed at applying this technology as embedded high pressure probes for transient shock events. Both approaches measure time resolved spectral shifts in the return light from short (few mm long) uniform FBGs at 1550 nm. In the first approach, we use a fiber coupled spectrometer to demultiplex spectral channels into an array (up to 12) of single element InGaAs photoreceivers. By monitoring the detectors during a shock impact event with high speed recording, we are able to track the pressure induced spectral shifting in FBG down to a time resolution of 20 ns. In the second approach, developed at the Special Technologies Lab, a coherent mode-locked fiber laser is used to illuminate the FBG sensor. After the sensor, wavelength-to-time mapping is accomplished with a chromatic dispersive element, and entire spectra are sampled using a single detector at the modelocked laser repetition rate of 50 MHz. By sampling with a 12 GHz InGaAs detector, direct wavelength mapping in time is recorded, and the pressure induced FBG spectral shift is sampled at 50 MHz. Here, the sensing systems are used to monitor the spectral shifts of FBGs that are immersed into liquid water and shock compressed using explosives. In this configuration, the gratings survive to pressures approaching 50 kbar. We describe both approaches and present the measured spectral shifts from the shock experiments.

Rodriguez, G.; Sandberg, R. L.; Lalone, B. M.; Marshall, B. R.; Grover, M.; Stevens, G.; Udd, E.

2014-06-01

94

Measurement of gas-phase sound speed and thermal diffusivity over a broad pressure range using laser-induced thermal acoustics  

Microsoft Academic Search

We report on the detection and analysis of signals generated from gas-phase laser-induced gratings over a large range of static pressure (0.04 -100 atm). We employed the experimental technique of laser-induced thermal acoustics and performed measurements on mixtures of NO 2 in air and CO 2 as a function of pressure. Accurate analysis of the acquired data was obtained from

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

1995-01-01

95

Reaction dynamics of V(a {sup 4}F{sub J})+NO{yields}VO(X {sup 4}{sigma}{sup -})+N studied by a crossed-beam laser-induced fluorescence technique  

SciTech Connect

The dynamics of the reaction, V(a {sup 4}F{sub J})+NO{yields}VO(X {sup 4}{sigma}{sup -})+N was studied by using a crossed-beam technique at 16.4 kJ/mol of collision energy. The V atomic beam was generated by laser vaporization and crossed with the O{sub 2} beam at a right angle. The laser-induced fluorescence (LIF) for the transition of VO(B {sup 4}{pi}-X {sup 4}{sigma}) was used to determine the rotational state distribution of the reaction product in the vibrational ground state. Almost pure V(a {sup 4}F{sub J}) beam was obtained by using the mixture of NH{sub 3} with N{sub 2} as a carrier gas. Comparing the LIF spectra of VO measured for two carrier gases, i.e., NH{sub 3}/N{sub 2} and pure N{sub 2}, it was concluded that the vibrational ground state of VO(X {sup 4}{sigma}{sup -}) is formed almost entirely from the reaction of V(a {sup 4}F{sub J}) and the contribution of the metastable V(a {sup 6}D{sub J}) is negligible. The observed rotational distribution was similar to a statistical prior prediction, and suggested that the title reaction proceeds via a long-lived intermediate, which is consistent with an electron transfer mechanism.

Ishida, M.; Yamashiro, R.; Matsumoto, Y.; Honma, Kenji [Department of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori, Hyogo 678-1297 (Japan)

2006-05-28

96

A fiber Bragg grating based tunable laser source for quasi-static and dynamic strain monitoring  

NASA Astrophysics Data System (ADS)

Fiber Bragg gratings (FBGs) are excellent tools for monitoring mechanical and thermal strains, and have widespread application in the structural health monitoring (SHM) of aerospace, civil, and mechanical structures. A common approach used for interrogating FBG sensors involves the illumination of the sensor with a broadband laser source and the narrowband reflected light reflected from the FBG is monitored with a wavelength sensitive optical detection system. The thermal or mechanical perturbations experienced by the FBG sensor lead to a shift in its reflectivity spectrum. In this work, an alternative interrogation scheme is presented that uses an FBG based narrowband tunable laser source produced by incorporating the FBG into a fiber ring laser cavity as an optical feedback element. The laser cavity consists an erbium doped fiber (EDF) connected to the FBG at the output of the fiber ring, which allows for the generation of the required amplified stimulated emission (ASE) in the C-band and lasing at the center wavelength of the FBG reflectivity spectrum. With this interrogation scheme, the wavelength of the resulting narrowband laser source tracks the center wavelength of the FBG sensor as it drifts due to quasi-static and/or dynamic mechanical and thermal strains. In addition, the instantaneous spectral line-width of the laser source is effectively narrowed owing to the long length of the laser cavity, which facilitates highly sensitive demodulation of dynamic shifts of the lasing wavelength with a high coherence optical interferometer.

Balogun, Oluwaseyi; Krishnaswamy, Sridhar

2009-03-01

97

Adaptive two-wave mixing wavelength demodulation of fiber Bragg grating sensor for monitoring dynamic strains  

NASA Astrophysics Data System (ADS)

A two-wave mixing (TWM) wavelength demodulator using InP:Fe photorefractive crystal (PRC) in the C-band (1530-1570nm) is demonstrated. The system can be used as a wavelength demodulator for use with Fiber Bragg Grating (FBG) sensors to monitor dynamic strains. In this configuration, the FBG is illuminated with a broadband source, and any strain in the FBG is encoded as a wavelength shift of the light reflected by the FBG. The reflected light from the FBG is spilt into two unbalanced paths and both beams (pump and signal) mix in the PRC. Any wavelength shift of the reflected light results in an equivalent phase shift between the pump and signal beams as they travel unbalanced path lengths. Since TWM is an adaptive process, the two interfering beams are naturally in quadrature and remain in quadrature even in the presence of large quasi-static strains. We demonstrate that FBG demodulation using TWM has the ability to selectively monitor dynamic strains without the need for active compensation of large quasi-static strains that otherwise would cause the FBG sensor to drift. As TWM interferometers can be readily multiplexed at relatively low cost; the proposed technique can be used to demodulate signals from a network of FBG sensors for use in structural health monitoring.

Qiao, Yi; Zhou, Yi; Krishnaswamy, Sridhar

2005-05-01

98

Fabrication sub-10nm metallic gratings with carbon nanotube - A study by molecular dynamics simulation method  

Microsoft Academic Search

In this research project we present a novel manufacturing process which is able to fabricate sub-10nm metallic gratings. It utilizes CNTs as a wire-cutting tool to remove the tiny metallic materials and fabricates the metallic gratings. The strategy is to embed the CNTs into the metallic material first, and then steer one ends of the CNTs upward with a constant

Ming-Chieh Cheng; Cheng-Kuo Sung

2011-01-01

99

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

100

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

E-print Network

inhomogeneity of In composition. Recently, InGaN/GaN-based light emitting diodes (LEDs) have been commercialized (3 nm) and a GaN cap (5 nm) layer. LED structure of GaN/InGaN SQW is composed of GaN (30 nm), nCarrier Dynamics in InGaN/GaN SQW Structure Probed by the Transient Grating Method

Okamoto, Koichi

101

Interrogation of a wavelength tunable fiber Bragg grating sensor based ring laser for dynamic strain monitoring  

NASA Astrophysics Data System (ADS)

Fiber Bragg gratings (FBGs) are wavelength selective optical reflectors with excellent strain sensitivity and small sensing footprint, which makes them suitable as diagnostic sensors for structural health monitoring applications. In this work, we explore the narrowband wavelength selectivity of FBGs for optical feedback in a tunable fiber ring laser. The fiber ring laser consists of an erbium doped fiber laser that is pumped with a Raman laser (980 nm) to produce population inversion and amplified spontaneous emission (ASE) in the C-band. The ASE light is used to illuminate a FBG sensor connected to the ring, and the reflected light from the sensor is fed back into the laser cavity to produce stimulated emission at the instantaneous center wavelength of the sensor. As the wavelength of the sensor shifts due mechanical or thermal strains, the wavelength of the optical output from the ring laser shifts accordingly. By combining the ring laser with a dynamic spectral demodulator for optical readout, the instantaneous wavelength of the ring laser is tracked with high temporal resolution. The fiber ring laser system offers several potential advantages in the diagnostic sensing of mechanical strains for SHM applications including, fully integrated laser and sensor system, high source power levels at the sensor wavelength, narrow spectral line-width, coherent spectral demodulation, and low system costs. In this work, we present experimental results that detail the feasibility of dynamic spectral tuning of the fiber ring laser at frequencies up to hundreds of kilohertz using a single FBG sensing element. Using multiple sensing elements, the fiber ring laser system would allow for active monitoring of dynamic strains in a multi-point sensor array configuration, which is particularly suitable for the localization of high frequency mechanical strains produced by impact loading and cracking events in structures.

Balogun, Oluwaseyi; Zhu, Yinian; Krishnaswamy, Sridhar

2010-03-01

102

Experimental investigation of the dynamics of laser-induced gas-plasma flows under femtosecond laser ablation of copper in vacuum  

NASA Astrophysics Data System (ADS)

Thermophysical and gas-dynamic characteristics of gas-plasma flows induced by ultrashort laser pulses interacting with a thin-film copper target in vacuum were studied experimentally. Using combined laser interferometry and complex processing of experimental data, we estimated the momentum coupling coefficient and the efficiency of laser-energy conversion to kinetic energy, spatiotemporal distributions of the number density and velocities of particles, pressure, and temperature in the gas-plasma flow. We provide comparative analysis of presented data with those found in the literature, which were obtained by other methods.

Loktionov, E. Yu.; Protasov, Yu. S.; Protasov, Yu. Yu.

2013-11-01

103

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

104

Dynamic, full-spectral interrogation of fiber Bragg grating sensors for impact testing of composite laminates  

Microsoft Academic Search

This paper presents the full-spectral measurement of fiber Bragg grating sensor responses during impact testing of composite laminates. The sensors are embedded in carbon fiber\\/epoxy laminates which are subjected to multiple low velocity impacts until perforation of the laminate occurs. Applying a recently developed high-speed interrogator, the Bragg grating sensor interrogation is demonstrated at 534 Hz over a 14.9 nm

A. Propst; K. Peters; M. A. Zikry; W. Kunzler; Z. Zhu; M. Wirthlin; R. Selfridge; S. Schultz

2009-01-01

105

Laser-induced breakdown spectroscopy combined with spatial heterodyne spectroscopy.  

PubMed

A spatial heterodyne spectrometer (SHS) is tested for the first time in combination with laser-induced breakdown spectroscopy (LIBS). The spectrometer is a modified version of the Michelson interferometer in which mirrors are replaced by diffraction gratings. The SHS contains no moving parts and the gratings are fixed at equal distances from the beam splitter. The main advantage is high throughput, about 200 times higher than that of dispersive spectrometers used in LIBS. This makes LIBS-SHS a promising technique for low-light standoff applications. The output signal of the SHS is an interferogram that is Fourier-transformed to retrieve the original plasma spectrum. In this proof-of-principle study, we investigate the potential of LIBS-SHS for material classification and quantitative analysis. Brass standards with broadly varying concentrations of Cu and Zn were tested. Classification via principal component analysis (PCA) shows distinct groupings of materials according to their origin. The quantification via partial least squares regression (PLS) shows good precision (relative standard deviation < 10%) and accuracy (within ± 5% of nominal concentrations). It is possible that LIBS-SHS can be developed into a portable, inexpensive, rugged instrument for field applications. PMID:25226262

Gornushkin, Igor B; Smith, Ben W; Panne, Ulrich; Omenetto, Nicoló

2014-09-01

106

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

107

On two optomechanical effects of laser-induced electrostriction in dielectric liquids  

NASA Astrophysics Data System (ADS)

This paper presents electrostriction from the phenomenological perspective, and gives details on two mechanical effects arising from laser-matter interaction. Electrostriction is the tendency of materials to compress in the presence of a varying electric field. In this paper, the investigated materials are polar and nonpolar dielectric liquids. It is stressed that the dominant factor is the time evolution of the laser pulse, which causes tensile stresses and acoustic waves. The study is supported by experimental realization of electrostriction, which can be detected only at favorable conditions (observed in water, but not in castor oil). This study will shed light in developing measurement techniques (e.g., laser-induced grating spectroscopy) and in explaining the onset of cavities and laser-induced liquid breakdown.

Gojani, Ardian B.; Bejtullahu, Rasim; Obayashi, Shigeru

2014-09-01

108

On two optomechanical effects of laser-induced electrostriction in dielectric liquids  

E-print Network

This paper presents electrostriction from the phenomenological perspective, and gives details on two mechanical effects arising from laser-matter interaction. Electrostriction is the tendency of materials to compress in the presence of a varying electric field. In this paper, the investigated materials are polar and nonpolar dielectric liquids. It is stressed that the dominant factor is the time evolution of the laser pulse, which causes tensile stresses and acoustic waves. The study is supported by experimental realization of electrostriction, which can be detected only at favourable conditions (observed in water, but not in castor oil). This study will shed light in developing measurement techniques (e.g., laser-induced grating spectroscopy) and in explaining the onset of cavities and laser-induced liquid breakdown.

Gojani, Ardian B; Obayashi, Shigeru

2014-01-01

109

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

110

Aerosol measurements with laser-induced breakdown spectroscopy  

E-print Network

laser-induced breakdown spectroscopy measurements, Applied Physics Letters,by giant-pulse laser. Applied Physics Letters, vol. 3, no.Laser-Induced Breakdown Spectroscopy Measurements,” Applied Physics Letters,

Lithgow, Gregg Arthur

2007-01-01

111

Study Of Laser-Induced Copolymerization  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

112

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

113

Dynamics of a stored Zeeman coherence grating in an external magnetic field  

E-print Network

We investigate the evolution of a Zeeman coherence grating induced in a cold atomic cesium sample in the presence of an external magnetic field. The gratings are created in a three-beam light storage configuration using two quasi-collinear writing laser pulses and reading with a counterpropagating pulse after a variable time delay. The phase conjugated pulse arising from the atomic sample is monitored. Collapses and revivals of the retrieved pulse are observed for different polarizations of the laser beams and for different directions of the applied magnetic field. While magnetic field inhomogeneities are responsible for the decay of the coherent atomic response, a five-fold increase in the coherence decay time, with respect to no applied magnetic field, is obtained for an appropriate choice of the direction of the applied magnetic field. A simplified theoretical model illustrates the role of the magnetic field mean and its inhomogeneity on the collective atomic response.

D. Moretti; D. Felinto; J. W. R. Tabosa; A. Lezama

2010-05-03

114

Demodulation of Fiber Bragg Grating Sensors Based on Dynamic Tuning of a Multimode Laser Diode  

Microsoft Academic Search

Dither demodulation of fiber Bragg grating sensors illuminated with multimode light from laser diodes is theoretically and experimentally investigated. Quasi-static temperature and strain sensitivities of 0.09 °Cy=Hz and 0.6 m?y=Hz are obtained. We show that it is possible to measure small ac signals that lie outside the feedback loop bandwidth by using a synchronous detection referenced to twice the dither

Luís Alberto Ferreira; Envangelos Vasilios Diatzikis; Jose Luis Santos; Faramarz Farahi

1999-01-01

115

Static and dynamic testing of bridges and highways using long-gage fiber Bragg grating based strain sensors  

NASA Astrophysics Data System (ADS)

Fiber optic Bragg gratings packaged in long gage configurations are being used to measure static and dynamic strain in structures and structural models to monitor structural health and predict damage incurred from a seismic event. These long gage sensors are being used to experimentally verify analytical models of post-earthquake evaluation based on system identification analysis. This fiber optic deformation measurement system could play a significant role in monitoring/recording with a higher level of completeness the actual seismic response of structures and in non-destructive seismic damage assessment techniques based on dynamic signature analysis. This new sensor technology will enable field measurements of the response of real structures to real earthquakes with the same or higher level of detail/resolution as currently in structural testing under controlled laboratory conditions.

Schulz, Whitten L.; Conte, Joel P.; Udd, Eric; Seim, John M.

2000-12-01

116

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

117

Origin of laser-induced near-subwavelength ripples: interference between surface plasmons and incident laser.  

PubMed

We show that short-pulse laser-induced classical ripples on dielectrics, semiconductors, and conductors exhibit a prominent "non-classical" characteristic-in normal incidence the periods are definitely smaller than laser wavelengths, which indicates that the simplified scattering model should be revised. Taking into account the surface plasmons (SPs), we consider that the ripples result from the initial direct SP-laser interference and the subsequent grating-assisted SP-laser coupling. With the model, the period-decreasing phenomenon originates in the admixture of the field-distribution effect and the grating-coupling effect. Further, we propose an approach for obtaining the dielectric constant, electron density, and electron collision time of the high-excited surface. With the derived parameters, the numerical simulations are in good agreement with the experimental results. On the other hand, our results confirm that the surface irradiated by short-pulse laser with damage-threshold fluence should behave metallic, no matter for metal, semiconductor, or dielectric, and the short-pulse laser-induced subwavelength structures should be ascribed to a phenomenon of nano-optics. PMID:20025303

Huang, Min; Zhao, Fuli; Cheng, Ya; Xu, Ningsheng; Xu, Zhizhan

2009-12-22

118

Laser-Induced Etching of Platinum with Chlorine with the Stimulated Wood's Anomaly.  

NASA Astrophysics Data System (ADS)

Laser-induced etching (LIE) rates were measured for the platinum-chlorine (Pt-Cl_2) LIE system, one of several metal-etchant gas systems surveyed which exhibited stimulated Wood's anomaly (SWA) gratings. Stereo and non-stereo photogrammetry was used to measure the LIE rates from scanning electron micrographs (SEM) in the LIE zone. The LIE reaction was modeled as the simultaneous, thermochemical Pt-Cl_2 reaction and Pt evaporation using kinetic data from the literature. The LIE zone temperature distribution was estimated from substrate temperature measurements and a model for the temperature rise induced by an incident Gaussian laser beam, to be up to 2540 K at the center of the beam, assuming the bulk reflectivity. The measured LIE rates were found to be 10-100 times faster than our model predicted, given the results from our thermal model. The measured LIE rates were not diffusion limited based upon these models. LIE zone temperature estimates obtained by fitting the measured LIE rates to the kinetic model were 250-450 K higher than obtained from our thermal model. This discrepancy can be corrected by assuming a decreased reflectivity in the LIE zone. We have experimentally demonstrated that the gratings formed during Pt-Cl_2 LIE are caused by the SWA, since the grating vector was always parallel to the electric field of the incident light and was otherwise independent of the etching parameters. A thermal model was developed for a Gaussian laser beam, sinusoidally modulated by interference; in the case of the SWA the interference is with a surface wave. We show that a steady state thermal grating can exist in the LIE zone. The relative peak-to -peak amplitude of the thermal grating at the origin of a 100% modulated Gaussian beam was estimated by our model at 12% under our conditions (d = 647.1 nm and w = 2.8 ?m). The amplitude of the modulation is proportional to d/w for d < w, where d is the period of the interference pattern and w is the 1/e^2 beam radius, whence strong steady-state thermal gratings are only expected in tightly focused beams. Although the details of the grating formation mechanism have not been proven, it seems more likely that it is a thermally driven process, rather than an electromagnetically driven one. On a molten surface the grating is formed by thermally induced surface tension gradients; on a solid surface, by thermally induced spatially modulated etch rates. The surface grating can then modify the thermal grating through both interaction with the incident beam and the local heat transport, forming a complex feedback loop.

Bumm, Lloyd A.

119

Laser induced fluorescence technique for environmental applications  

NASA Astrophysics Data System (ADS)

We discuss the development of laser induced fluorescence sensors and their application in the evaluation of water pollution and physiological status of higher plants and algae. The sensors were built on the basis of reliable and robust solid-state Nd:YAG lasers. They demonstrated good efficiency in: i) detecting and characterizing oil spills and dissolved organic matter; ii) evaluating the impact of stress on higher plants (cork oak, maritime pine, and genetically modified Arabidopsis); iii) tracking biomass changes in intertidal microphytobenthos; and iv) mapping macroalgal communities in the Tagus Estuary.

Utkin, Andrei B.; Felizardo, Rui; Gameiro, Carla; Matos, Ana R.; Cartaxana, Paulo

2014-08-01

120

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

121

Laser Induced Chemical Liquid Phase Deposition (LCLD)  

SciTech Connect

Laser induced chemical deposition (LCLD) of metals onto different substrates attracts growing attention during the last decade. Deposition of metals onto the surface of dielectrics and semiconductors with help of laser beam allows the creation of conducting metal of very complex architecture even in 3D. In the processes examined the deposition occurs from solutions containing metal ions and reducing agents. The deposition happens in the region of surface irradiated by laser beam (micro reactors). Physics -chemical reactions driven by laser beam will be discussed for different metal-substrate systems. The electrical, optical, mechanical properties of created interfaces will be demonstrated also including some practical-industrial applications.

Nanai, Laszlo; Balint, Agneta M. [University of Szeged, JGYPK, Department of General and Environmental Physics H-6725 Szeged, Boldogasszony sgt. 6 (Hungary); West University of Timisoara, Faculty of Physics, Department of Physics, Bulv. V. Parvan 4, Timisoara 300223 (Romania)

2012-08-17

122

Standoff Laser Induced Fluorescence Sensors for Biological Warfare Agents  

Microsoft Academic Search

We report comparison studies of two different sensors, Gated Intensified charge coupled device and Multi Anode Photo Multiplier Tube Detector for Standoff detection of bio-aerosol. Ultraviolet Laser Induced Fluorescence technique is considered. Ultraviolet Laser Induced Fluorescence signals are evaluated under different bacteria aerosol concentration, range, atmospheric condition and solar background. Signal to Noise ratio is calculated for both the detectors

Deepak Kumar; Ramesh C. Sharma; Anil Kr Maini

2012-01-01

123

Fabrication of Twisted Nematic Gratings Using Polarization Hologram Based on Azo-Dye-Doped Liquid Crystals  

NASA Astrophysics Data System (ADS)

This study establishes the feasibility of fabricating twist nematic gratings (TN-gratings) using a polarization holographic approach on the basis of the laser-induced adsorption of azo dyes by a polymer-coated glass substrate. This holographic recording is fast, and the formed TN gratings are permanent. Measurements indicate that the first-order diffracted-beam intensity from this TN grating is independent of the polarization of the incident beam. The polarization states of the zeroth- and first-order diffracted beams are perpendicular to each other. The polarization state and intensity distribution of the diffracted beams agree well with their theoretical values derived using the Jones matrix.

Wu, Shing-Trong; Chen, Yi Shin; Guo, Jian Hong; Fuh, Andy Ying-Guey

2006-12-01

124

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

125

Laser-induced autofluorescence of caries  

NASA Astrophysics Data System (ADS)

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

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

1993-07-01

126

Mapping of intermodal beat length distribution in an elliptical-core two-mode fiber based on Brillouin dynamic grating.  

PubMed

Distributed measurement and characterization of the intermodal beat length between LP(01) and LP(11) modes in an elliptical-core (e-core) two-mode fiber (TMF) are demonstrated by the analysis of Brillouin dynamic grating (BDG) spectra. The BDG is generated by the stimulated Brillouin scattering (SBS) of the LP(01) mode and probed by the LP(11) mode, with four different pairs of the spatial and polarization modes in the e-core TMF applied for the pump and the probe (LP(01)x-LP(11)y, LP(01)y-LP(11)y, LP(01)x-LP(11)x, and LP(01)y-LP(11)x). A mode selective coupler (MSC) is used for selective launch and retrieval of the LP(01) and the LP(11) modes in the BDG operation, and the local reflection spectra from the BDG are obtained by an optical time-domain analysis. A distribution map of the intermodal beat length is acquired for each pair of the pump-probe modes with a 1.5 m spatial resolution along a 75 m e-core TMF. Temperature- and strain-dependence of the BDG spectrum is also evaluated for each case. PMID:25090543

Kim, Yong Hyun; Song, Kwang Yong

2014-07-14

127

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

Microsoft Academic Search

Volume diffractive gratings (Bragg gratings) in photo-thermo-refractive (PTR) inorganic glass are proposed for incoherent laser beam combining because they have narrow spectral selectivity and diffraction efficiency greater than 95% from visible to near IR regions. They showed no laser-induced damage, no thermal lens, and no Bragg angle shift under CW Yb-fiber laser (1096 nm) irradiation at 100 kW\\/cm2. It opens

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

2003-01-01

128

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

PubMed

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

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

2012-01-01

129

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

130

Laser-induced fluorescence in medical diagnostics  

NASA Astrophysics Data System (ADS)

We have performed extensive investigations using laser-induced fluorescence in animal as well as human tissue in order to localize diseased tissue and thus discriminate such tissue from normal surrounding areas. In characterizing different tissue types the endogenous fluorescence (autofluorescence) as well as specific fluorescence from different photosensitising substances was utilized. We have investigated different experimental and human malignant tumors in vivo and in vitro as well as atherosclerotic lesions in vitro. A fiber-optic fluorosensor was constructed and used in the experiments and in the clinical examination of patients. Dimensionless spectroscopic functions were formed to ensure that the signals were independent of clinically uncontrollable variables such as distance variations, tissue topography, light source fluctuations and variations in detection efficiency. A multi-color two-dimensional imaging system was constructed for real-time imaging. The system was tested peroperatively and during standard examination patient procedures. Besides utilizing the time-integrated fluorescence signal we have also investigated the possibility of incorporating time-resolved fluorescence characterization.

Andersson-Engels, Stefan; Johansson, Jonas; Svanberg, Katarina; Svanberg, Sune

1990-07-01

131

Laser-induced lipolysis on adipose cells  

NASA Astrophysics Data System (ADS)

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

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

2004-10-01

132

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

NASA Technical Reports Server (NTRS)

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

Tai, Hsiang

2006-01-01

133

Degenerate two-wave mixing via a dynamic grating in Fe{sub 3}O{sub 4} nanoparticle suspensions  

SciTech Connect

Optical-gradient-force-induced spatially inhomogeneous disturbances of the dielectric permittivity of a suspension of spherical nanoparticles are analysed in the Maxwell Garnett approximation. Degenerate two-wave mixing in such media is shown to cause the formation of a spatial nanoparticle grating and the associated permittivity grating in the colloid. Relations are derived for the complex coupling constant of the waves. Codirectional and contradirectional two-wave mixing in suspensions of light-absorbing nanoparticles is considered. The two-beam coupling gain at 640 nm in various suspensions of Fe{sub 3}O{sub 4} nanoparticles may reach {approx}10 cm{sup -1}. (nonlinear optical phenomena)

Ageev, E Yu; Litvinov, Rudol'f V; Khat'kov, N D [Tomsk State University of Control Systems and Radioelectronics, Tomsk (Russian Federation); Zagrebin, L V; Shestov, S S [Center for Information and Cell Medicine, Ltd, Moscow (Russian Federation)

2009-05-31

134

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

135

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

136

Laser induced surface modification of aluminum alloys  

NASA Astrophysics Data System (ADS)

Purpose of this work is to improve surface related properties of aluminum alloys by employing laser. Two approaches were taken to achieve this goal. First approach involves a rapid solidification induced by laser. A high power laser was used to melt the surface layer of A319. In-situ high-speed infrared thermographs captured during laser surface melting of A319 enabled estimation of maximum temperature, temperature gradient and cooling rate. The cooling rate thus estimated provided a range of cell size that closely matched with the experimentally observed cell size. The high cooling rate (>105) resulted in extensive refinement of microstructure in the laser-melted layer. Instrumented indentation technique was used to measure hardness (H) and elastic modulus (E) of the laser-melted layer. Berkovich tip was used to indent the material for 100-nm, 200-nm, 500-nm, and 1000-nm depths. The H and the E were found to be 1.22 GPa and 78.2 GPa, respectively, for 1000-nm indentation depths. The variances associated with H and E were minimal. Also, H and E increased with decreasing depth of indentation. Closer examination suggested that when the heterogeneity in the material was in the scale of indentation depth, significant scattering took place and the hard phase Si influenced the average hardness. The improvement in mechanical properties manifested in better wear resistance. In second approach, laser was used for coating of iron oxide on A319 to produce a Fe3O4/Al reaction composite coating. Infrared thermography was employed thermal studies. Electron microscopy indicated reactions between oxide particles and aluminum-forming Fe-Al intermetallics, Al 2O3, and various intermediate products. Analysis of the coating, fractured in vacuuo, indicated substantial toughness of the material due to extremely refined microstructure with finely distributed reaction products and strong interfacial bonding between particles and the matrix. Mechanical properties of the coating were evaluated by instrumented indentation techniques. Hardness and elastic modulus values were found to be uniform at 1.24 and 76 GPa, respectively. No radial cracking was observed for either the Berkovich or cube-corner indenters. These results indicate that the laser-induced rapidly solidified composite material is tough and fracture resistant.

Nayak, Subhadarshi

137

Wavelength dependence of laser-induced retinal injury  

NASA Astrophysics Data System (ADS)

The threshold for laser-induced retinal damage is dependent primarily upon the laser wavelength and the exposure duration. The study of the wavelength dependence of the retinal damage threshold has been greatly enhanced by the availability of tunable lasers. The Optical Parametric Oscillator (OPO), capable of providing useful pulse energy throughout a tuning range from 400 nm to 2200 nm, made it possible to determine the wavelength dependence of laser-induced retinal damage thresholds for q-switched pulses throughout the visible and NIR spectrum. Studies using the a tunable TI:Saph laser and several fixed-wavelength lasers yielded threshold values for 0.1 s exposures from 440 nm to 1060 nm. Laser-induced retinal damage for these exposure durations results from thermal conversion of the incident laser irradiation and an action spectrum for thermal retinal damage was developed based on the wavelength dependent transmission and absorption of ocular tissue and chromatic aberration of the eye optics. Long (1-1000s) duration exposures to visible laser demonstrated the existence of non-thermal laser-induced retinal damage mechanisms having a different action spectrum. This paper will present the available data for the wavelength dependence of laser-induced thermal retinal damage and compare this data to the maximum permissible exposure levels (MPEs) provided by the current guidelines for the safe use of lasers.

Lund, David J.; Edsall, Peter; Stuck, Bruce E.

2005-04-01

138

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

139

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

140

Laser induced breakdown spectroscopy inside liquids: Processes and analytical aspects  

NASA Astrophysics Data System (ADS)

This paper provides an overview of the laser induced breakdown spectroscopy (LIBS) inside liquids, applied for detection of the elements present in the media itself or in the submerged samples. The processes inherent to the laser induced plasma formation and evolution inside liquids are discussed, including shockwave generation, vapor cavitation, and ablation of solids. Types of the laser excitation considered here are single pulse, dual pulse and multi-pulse. The literature relative to the LIBS measurements and applications inside liquids is reviewed and the most relevant results are summarized. Finally, we discuss the analytical aspects and release some suggestions for improving the LIBS sensitivity and accuracy in liquid environment.

Lazic, V.; Jovi?evi?, S.

2014-11-01

141

Evolution of laser-induced plasma in solvent aerosols  

NASA Astrophysics Data System (ADS)

This paper describes a novel technique for the detection of contaminants in air using the process of laser-induced filamentation. This work is focused primarily on the visible and infrared spectrum. Characterization of the temporal and spatial evolution of laser-generated plasma in solvent aerosols is necessary for the development of potential applications. Atmospheric aerosols impact capabilities of applications such as range from laser-induced ionized micro channels and filaments able to transfer high electric pulses over a few hundreds of meters, to the generation of plasma artifacts in air, far away from the laser source.

Hening, Alexandru; Wroblewski, Ronald; George, Robert; McGirr, Scott

2014-10-01

142

Holographic Grating Formation in Cationic Photopolymers with Dark Reaction  

Microsoft Academic Search

We propose a new formula to describe the dynamics of holographic grating formation under low intensity pulse exposures in cationic photopolymers, in which the dark reaction contributes dominantly to the grating strength. The formula is based on the living polymerization mechanism and the diffusion-free approximation. The analytical solution indicates that the grating formation time depends on the termination rate constant,

Hao-Yun Wei; Liang-Cai Cao; Claire Gu; Zhen-Feng Xu; Ming-Zhao He; Qing-Sheng He; Shu-Rong He; Guo-Fan Jin

2006-01-01

143

Analysis of Laser-Induced Plume During Disk Laser Welding at Different Speeds  

NASA Astrophysics Data System (ADS)

During high power disk laser welding, the high-speed photography was used to measure the dynamic images of the laser-induced plume at different laser welding speeds. Various plume features (area, height and brightness) were extracted from the images by the color space clustering algorithm. Combined with observation on the surface and the cross sections of welding samples, the effect of welding speed on welding stability was analyzed. From the experimental results, it was found that these features of plume could reflect the welding state. Thus changes of the plume features corresponded to different welding speeds, which was helpful for monitoring the laser welding stability.

Wang, Teng; Gao, Xiangdong; Katayama, Seiji

2013-08-01

144

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

145

Quasi-distributed measurement on femtosecond laser-induced scattering voids using incoherent OFDR and OTDR  

NASA Astrophysics Data System (ADS)

We propose to use focused femtosecond laser pulses to create scattering damage in standard singlemode optical fibres as reference points for quasi-distributed sensing applications. Such sensor fibres are interrogated with incoherent optical frequency domain reflectometry (I-OFDR) technique and optical time domain reflectometry (OTDR). A performance comparison of both techniques with the clear advantage of the I-OFDR is presented as well as a quasi-distributed length change measurement application. Also dynamic measurement based on the I-OFDR technique is demonstrated on a femtosecond laser-induced sensor chain.

Liehr, Sascha; Burgmeier, Jörg

2013-05-01

146

Laser induced heat source distribution in bio-tissues  

NASA Astrophysics Data System (ADS)

During numerical simulation of laser and tissue thermal interaction, the light fluence rate distribution should be formularized and constituted to the source term in the heat transfer equation. Usually the solution of light irradiative transport equation is given in extreme conditions such as full absorption (Lambert-Beer Law), full scattering (Lubelka-Munk theory), most scattering (Diffusion Approximation) et al. But in specific conditions, these solutions will induce different errors. The usually used Monte Carlo simulation (MCS) is more universal and exact but has difficulty to deal with dynamic parameter and fast simulation. Its area partition pattern has limits when applying FEM (finite element method) to solve the bio-heat transfer partial differential coefficient equation. Laser heat source plots of above methods showed much difference with MCS. In order to solve this problem, through analyzing different optical actions such as reflection, scattering and absorption on the laser induced heat generation in bio-tissue, a new attempt was made out which combined the modified beam broaden model and the diffusion approximation model. First the scattering coefficient was replaced by reduced scattering coefficient in the beam broaden model, which is more reasonable when scattering was treated as anisotropic scattering. Secondly the attenuation coefficient was replaced by effective attenuation coefficient in scattering dominating turbid bio-tissue. The computation results of the modified method were compared with Monte Carlo simulation and showed the model provided reasonable predictions of heat source term distribution than past methods. Such a research is useful for explaining the physical characteristics of heat source in the heat transfer equation, establishing effective photo-thermal model, and providing theory contrast for related laser medicine experiments.

Li, Xiaoxia; Fan, Shifu; Zhao, Youquan

2006-09-01

147

Mechanisms of laser induced reactions in opaque heterogeneous environments  

NASA Astrophysics Data System (ADS)

The technique of laser flash photolysis has been applied to both heterogeneous and homogeneous samples in order to increase understanding of the mechanisms of laser induced reactions at surfaces. Nanosecond diffuse reflectance laser flash photolysis has been used to study triplet state absorption and fluorescence emission of monomers and dimers of acridine orange and other dyes which are shown to aggregate when adsorbed on microcrystalline cellulose and on other surfaces. The properties of excited states within dyed fabrics have been evaluated in several cases. The mechanism of the yellowing of thermomechanical paper pulp has also been investigated and transients studied on nanosecond timescales for the first time. Triplet-triplet energy transfer from benzophenone to oxazine dyes, from eosin to anthracene, and from anthracene to azomethine dyes has been studied on both cellulose and silica surfaces. This work demonstrates the occurrence of energy transfer by static and dynamic mechanisms depending on both the nature of the surface and the adsorbed species. The first picosecond studies exciting directly into the charge transfer absorption bands of aromatic hydrocarbon/oxygen complexes formed in the presence of high pressures of oxygen have been carried out to demonstrate the role of charge-transfer interactions in determining the singlet oxygen formation efficiencies during quenching of electronically excited states by molecular oxygen. Nanosecond laser excitation of a series of naphthalene and anthracene derivatives in the presence and absence of oxygen has clearly demonstrated for the first time the importance of charge transfer interactions in determining oxygen quenching constants and singlet oxygen formation efficiencies.

Wilkinson, F.

1993-11-01

148

Holographic Gratings for Optical Processing  

NASA Technical Reports Server (NTRS)

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

Kukhtarev, Nickolai

2002-01-01

149

LIBS vs TRELIBS - The Relative Merits Of Laser-Induced Breakdown Spectroscopy Versus Time Resolved Laser-Induced Breakdown Spectroscopy  

NASA Astrophysics Data System (ADS)

LIBS - Laser-Induced Breakdown Spectroscopy - and TRELIBS - Time REsolved Laser-Induced Breakdown Spectroscopy - are relatively new techniques for obtaining analytical emissions from solid, liquid and gaseous samples. A pulsed laser is focused on the surface of a solid or liquid sample or focused in a gaseous sample, creating a transient plasma. Sample analytes emit characteristic radiation for upwards to tens of micro-seconds. The event is monitored spectrophotometically using LIBS, where the whole event is analyzed, or by TRELIBS, where the time resolution of the plasma event is analyzed.

Cadwell, L.; Belliveau, J.; Huwell, L.; Griffin, H.

1986-07-01

150

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

PubMed

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

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

2011-01-01

151

Characterization of fatigue damage in adhesively bonded lap joints through dynamic, full-spectral interrogation of fiber Bragg grating sensors: 1. Experiments  

NASA Astrophysics Data System (ADS)

In this study we measure the in situ response of a fiber Bragg grating (FBG) sensor embedded in the adhesive layer of a single composite lap joint, subjected to harmonic excitation after fatigue loading. After a fully reversed cyclic fatigue loading is applied to the composite lap joint, the full-spectral response of the sensor is interrogated at 100 kHz during two loading conditions: with and without an added harmonic excitation. The full-spectral information avoided dynamic measurement errors often experienced using conventional peak wavelength and edge filtering techniques. The short-time Fourier transform (STFT) is computed for the extracted peak wavelength information to reveal time-dependent frequencies and amplitudes of the dynamic FBG sensor response. The dynamic response of the FBG sensor indicated a transition to strong nonlinear dynamic behavior as fatigue-induced damage progressed. The ability to measure the dynamic response of the lap joint through sensors embedded in the adhesive layer can provide in situ monitoring of the lap joint condition.

Webb, S.; Shin, P.; Peters, K.; Zikry, M. A.; Stan, N.; Chadderdon, S.; Selfridge, R.; Schultz, S.

2014-02-01

152

Laser induced electron acceleration in vacuum K. P. Singha)  

E-print Network

is abruptly stopped by a thin foil, the highly energetic electrons will continue to move forward inertially energetic electrons continue to move forward iner- tially and escape from the pulse, as well as the targetLaser induced electron acceleration in vacuum K. P. Singha) Department of Physics, Indian Institute

Singh, Kunwar Pal

153

Using Laser-Induced Incandescence To Measure Soot in Exhaust  

NASA Technical Reports Server (NTRS)

An instrumentation system exploits laser-induced incandescence (LII) to measure the concentration of soot particles in an exhaust stream from an engine, furnace, or industrial process that burns hydrocarbon fuel. In comparison with LII soot-concentration-measuring systems, this system is more complex and more capable.

Bachalo, William D.; Sankar, Subramanian V.

2005-01-01

154

Laser-induced breakdown spectroscopy based deminers' probe  

Microsoft Academic Search

We report on a prototype Laser Induced Breakdown Spectroscopy (LIBS) Deminers' Probe used to identify underground objects. We have built a prototype, and are in the process of developing a more advanced LIBS based Deminer' s Probe used to prod objects underground, and then sense them by creating a micro-plasma plume of the surface material and analyzing the spectrum of

James P. Hauck; Mark Walker; Siavosh Hamadani; Natalie Bloomhardt; Justin Eagan

2009-01-01

155

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

156

Diffraction gratings for optical sensing  

NASA Astrophysics Data System (ADS)

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

Lu, Patrick P.

157

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

158

Diffractive coherence in multilayer dielectric gratings  

SciTech Connect

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

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

1995-05-26

159

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

PubMed Central

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

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

2014-01-01

160

High-speed machining of glass materials by laser-induced plasma-assisted ablation using a 532-nm laser  

NASA Astrophysics Data System (ADS)

In this communication, we report a high-speed machining of glass materials by a novel laser ablation technique using a conventional visible laser for the first time. A high-quality micrograting structure is fabricated in fused quartz by laser-induced plasma-assisted ablation (LIPAA) using a second harmonic of Q-switched Nd+:YAG laser (532 nm). The plasma generated from a silver (Ag) target by the laser irradiation effectively assists in ablation of the fused quartz substrate by the same laser beam, although the laser beam is transparent to the substrate. A grating with a cross-sectional shape like a square-wave (period 20 ?m) is achieved using the mask projection technique. The ablation rate reaches several tens nm/pulse. In addition, LIPAA is applied to high-speed hole drilling (700 ?m in diameter) of fused-quartz (0.5 mm thick) and Pyrex glass (0.5 mm thick).

Zhang, J.; Sugioka, K.; Midorikawa, K.

161

Laser Induced Reverse Transfer with metal and hybrid material prepared with sol-gel process used on glass substrate  

NASA Astrophysics Data System (ADS)

This article presents a possible use of Laser Induced Reverse Transfer (LIRT) for metal deposition combined with hybrid material prepared using the sol-gel process. The goal was to obtain two dimensional metal gratings with inorganic-organic hybrid material protection on low cost glass substrates. The hybrid material using the sol-gel material is employed here to give better adhesion of metal deposited by LIRT on glass substrates, and also to possibly cover the metal structure. The hybrid material was an organically modified silicate glass based on methacryloxypropyltri-methoxysilane (MATPMS) and zirconium propoxide. The proposed process permits to prototype rapidly small diffractive structure in amplitude mode or to mark two dimensional complicated patterns without complex technologies employing a focalized and computer controlled Nd-YAG laser at 1064 nm. The different steps of the technology are also discussed.

Flury, Manuel; Pédri, Claude

2013-08-01

162

Laser-induced destruction of plasticized polymethylmethacrylate  

NASA Astrophysics Data System (ADS)

The resistance of PMMA with various concentrations of dibutyl phthalate plasticizer to Nd-laser radiation at a wavelength of 1.06 microns and a pulse duration of 30 ns was studied experimentally. The concentration of centers responsible for destruction is calculated, and the switch-on dynamics of matrix absorption connected with thermoelastic stresses is analyzed. Inhomogeneity absorption coefficients and matrix absorption under optical breakdown (OB) are calculated. The dependence of the OB intensity on the plasticizer concentration is related to the blocking of 'bridge' bonds by the plasticizer molecules. The results are pertinent to the use of PMMA as an optical material for lasers.

Genkin, V. N.; Izvozchikova, V. A.; Kitai, M. S.; Mylnikov, M. Iu.

1985-11-01

163

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

164

Polymer micro-fiber Bragg grating.  

PubMed

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

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

2013-09-01

165

Theoretical analysis and experimental evaluation of laser-induced interstitial thermotherapy in ex vivo porcine pancreas.  

PubMed

Laser-induced interstitial thermotherapy (LITT) has been recently applied to pancreas in animal models for ablation purpose. Assessment of thermal effects due to the laser-pancreatic tissue interaction is a critical factor in validating the procedure feasibility and safety. A mathematical model based on bioheat equation and its experimental assessment was developed. The LITT procedure was performed on 40 ex vivo porcine pancreases, with an Nd:YAG (1064 nm) energy of 1000 J and power from 1.5 up to 10 W conveyed by a quartz optical fiber with 300 ?m diameter. Six fiber Bragg grating sensors have been utilized to measure temperature distribution as a function of time at fixed distances from the applicator tip within pancreas undergoing LITT. Simulations and experiments show temperature variations ? T steeply decreasing with distance from the applicator at higher power values: at 6 W, ?T > 40 °C at 5 mm and ? T is approximately equal to 5 °C at 10 mm. ? T nonlinearly increases with power close to the applicator. Ablated and coagulated tissue volumes have also been measured and experimental results agree with theoretical ones. Despite the absence of data in the current literature on pancreas optical parameters, the model allowed a quite good prediction of thermal effects. The prediction of LITT effects on pancreas is necessary to assess laser dosimetry. PMID:22929361

Saccomandi, Paola; Schena, Emiliano; Caponero, Michele Arturo; Di Matteo, Francesco Maria; Martino, Margareth; Pandolfi, Monica; Silvestri, Sergio

2012-10-01

166

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

167

Laser-induced ultrafast demagnetization in ferromagnetic metals  

NASA Astrophysics Data System (ADS)

The laser-induced femtosecond demagnetization in ferromagnetic metals is investigated theoretically. Different from the conventional nanosecond one, which has long been considered as the speed limit of magnetic recording, this ultrafast demagnetization occurs during only some tens of femtoseconds. Even on these timescales, the demagnetization is genuine and, contrary to the conventional one, results from a cooperative effect of the laser field and the internal spin-orbit coupling. The spin-orbit coupling smears out the original identities of triplets and singlets while the laser field uses this as an avenue for demagnetization. This result follows from the nonperturbative (in the laser field) solution of the time-dependent Schrödinger equation. Moreover, our Hamiltonian contains the Ni bandstructure, on-site electron-electron interaction, and spin-orbit coupling. We find that, within certain limits but with realistic laser fluences, this laser-induced demagnetization can be manipulated controllably, an essential point to future applications.

Huebner, Wolfgang; Zhang, Guoping

2000-03-01

168

Laser-Induced Incandescence of Soot at High Pressures  

NASA Astrophysics Data System (ADS)

Measurements of soot emission properties are of interest in both fundamental research and combustion-based industries. Laser-induced incandescence of soot particles is a novel technique that allows unobtrusive measurements of both soot volume fraction and particulate size with significant advantages. An apparatus utilizing this technique has been customized and used to provide measurements of soot concentration and particle sizing of a laminar, diffusion methane/air flame at pressures of 10, 20 and 40 atm at 6 mm above the burner. Soot volume fraction measurements correlate well with literature findings at all pressures. Despite similar trends, particle size values are found to be consistently larger than values reported in literature. Discussion on the errors of laser-induced incandescence as well as recommendations for improving the apparatus and results are herein.

Ghasemi, Sanaz

169

Dynamics of laser-induced surface phase explosion in silicon  

SciTech Connect

Time-resolved ultrasonic studies revealed a second, delayed ablative pressure pulse after the first primary plasma pressure pulse in a silicon wafer irradiated by a UV nanosecond laser. The intensity-dependent delay time for the second pulse indicates the existence of a corresponding intensity-dependent homogeneous vapor bubble nucleation time in the superheated molten silicon prior to its phase explosion and ablative removal, since the integral pressure correlates with the ablation rate. A transient hot ablative plasma with calculated peak temperature {approx}30-90 eV and pressure {approx}20-110 GPa is suggested to superheat the bulk silicon via short-wavelength recombination and Bremsstrahlung emission.

Kudryashov, Sergey I. [P.N. Lebedev Physical Institute, Russian Academy of Sciences, 119991 Moscow (Russian Federation); Paul, Stanley; Lyon, Kevin; Allen, Susan D. [Department of Chemistry and Physics, Arkansas State University, State University, Arkansas 72467 (United States)

2011-06-20

170

Laser induced tuning of cholesteric liquid crystal without alignment layers  

NASA Astrophysics Data System (ADS)

We demonstrate a laser induced tuning effect on non-chiral azobenzene-doped CLC (Azo-CLCs) without using orientated substrate. The reversible tuning range is 90 nm under alternative violet (405 nm) and green (532 nm) laser exposure corresponded to the response time of 3 and 15 s, respectively. The current demonstrations may find applications in photoactive micro- or nano-photonic devices where orientated substrate is difficult to be incorporated.

Cheng, M.-C.; Huang, T.-C.; Lee, C.-Y.; Hsiao, Vincent K. S.

2014-12-01

171

Laser induced foaming and chemical modifications of gelatine films  

Microsoft Academic Search

This paper reports on the investigation of the microfoaming and chemical modifications following single-pulse laser irradiation conducted at 248nm (KrF excimer laser, 20ns fwhm) and at 266 and 355nm (Nd:YAG laser 4th and 3rd harmonic, 6ns fwhm) of gelatine films. Fluorescence emissions of the films were studied by laser induced fluorescence and spectrofluorimetry and the emission lifetimes were measured by

S. Gaspard; M. Oujja; C. Abrusci; F. Catalina; S. Lazare; J. P. Desvergne; M. Castillejo

2008-01-01

172

Laser-induced incandescence applied to droplet combustion  

NASA Astrophysics Data System (ADS)

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

Wal, Randall L. Vander; Dietrich, Daniel L.

1995-02-01

173

Coherent microwave radiation from a laser induced plasma  

SciTech Connect

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. [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544-5263 (United States)

2012-12-24

174

Laser-induced incandescence applied to droplet combustion  

NASA Technical Reports Server (NTRS)

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

VanderWal, Randall L.; Dietrich, Daniel L.

1995-01-01

175

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

176

Transient phonon vacuum squeezing due to femtosecond-laser-induced bond hardening  

NASA Astrophysics Data System (ADS)

Ultrashort optical pulses can be used both to create fundamental quasiparticles in crystals and to change their properties. In noble metals, femtosecond lasers induce bond hardening, but little is known about its origin and consequences. Here we simulate ultrafast laser excitation of silver at high fluences. We compute laser-excited potential-energy surfaces by all-electron ab initio theory and analyze the resulting quantum lattice dynamics. We also consider incoherent lattice heating due to electron-phonon interactions using the generalized two-temperature model. We find phonon hardening, which we attribute to the excitation of s electrons. We demonstrate that this may result in phonon vacuum squeezed states with an optimal squeezing factor of ˜0.001 at the L-point longitudinal mode. This finding implies that ultrafast laser-induced bond hardening may be used as a tool to manipulate the quantum state of opaque materials, where, so far, the squeezing of phonons below the zero-point motion has only been realized in transparent crystals by a different mechanism. On the basis of our finding, we further propose a method for directly measuring bond hardening.

Cheenicode Kabeer, Fairoja; Grigoryan, Naira S.; Zijlstra, Eeuwe S.; Garcia, Martin E.

2014-09-01

177

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

178

Biomedical application of laser-induced tissue oxygenation  

NASA Astrophysics Data System (ADS)

Concentration of oxygen in tissue plays an important role in enhancing in vivo wide variety of biochemical reactions including cell metabolism. Aerobic cell metabolism is primary mechanism in energy production in tissue. Controlling this mechanism gives unique possibility of biological stimulation to reach therapeutic effect. This goal could be reached by laser-induced photodissociation of oxyhemoglobin in cutaneous blood vessels. This phenomenon is considered as a main mechanism of biostimulating and therapeutic effect of low energy laser radiation. Laser-induced photodissociation of oxyhemoglobin in vivo manifests itself through the changes of the value of arterial blood saturation before and during the laser irradiation. High sensitive pulse oxymeter could be used for the measurements of the level of arterial blood saturation. Unique possibility is reached in local increase the concentration of oxygen by additional releasing it into tissue. Laser-induced enrichment of tissue oxygenation stimulates of cell metabolism and allows develop new effective methods for laser therapy as well as phototherapy of pathologies where elimination of local tissue hypoxia is critical.

Asimov, M. M.

2007-03-01

179

Laser-Induced Modification Of Energy Bands Of Transparent Solids  

SciTech Connect

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

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

2010-10-08

180

Optical nonlinearity of organic dyes as studied by Z-scan and transient grating techniques  

Microsoft Academic Search

The excited state absorption cross-section of 5,5?-dichloro-11-diphenyl-amino-3,3?-diethyl-10, 12-ethylinethiatricarbocyanine\\u000a perchlorate (IR140) have been measured by using a single beam transmission technique. Z-scan experiments have been used to find out a few nonlinear\\u000a parameters. The excited state relaxation times have also been measured by using laser induced transient grating (LITG) technique.

Umakanta Tripathy; R. Justin Rajesh; Prem B. Bisht; A. Subrahamanyam

2002-01-01

181

A fiber optic Bragg grating seismic sensor  

NASA Astrophysics Data System (ADS)

Here we present a fiber optic seismic waves sensor based on in-fiber Bragg gratings. Fiber Bragg Grating sensors have been demonstrated to have very high sensitivity to dynamical strain in the sub-micro-strain range and very extended dynamical response from static to very high frequency. The seismic sensing system is based on the integration of three FBGs dynamical strain sensors in a mechanical structure acting as an inverse pendulum. Polar symmetry of the mechanical system and 120° placement of the FBG sensors guarantee a directional capability of the seismic sensor. Design, manufacturing and preliminary dynamical testing of the seismic sensor are discussed.

Laudati, A.; Mennella, F.; Esposito, M.; Cusano, A.; Giordano, M.; Breglio, G.; Sorge, S.; Calisti Tassini, C.; Torre, A.; D'Altrui, G.; Cutolo, A.

2007-07-01

182

Characterization of fatigue damage in adhesively bonded lap joints through dynamic, full-spectral interrogation of fiber Bragg grating sensors: 2. Simulations  

NASA Astrophysics Data System (ADS)

In this paper, we simulate the response of fiber Bragg grating (FBG) sensors embedded in the adhesive layer of a composite lap that is subjected to harmonic excitation. To simulate accumulated fatigue damage at the adhesive layer, two forms of numerical nonlinearities are introduced into the model: (1) progressive plastic deformation of the adhesive and (2) changing the boundary of an interfacial defect at the adhesive layer across the overlap shear area. The simulation results are compared with previous measurements of the dynamic, full-spectral response of such FBG sensors for condition monitoring of the lap joint. Short-time Fourier transforms (STFT) of the locally extracted axial strain time histories reveal a transition to nonlinear behavior of the composite lap joint by means of intermittent frequencies that were observed in the experimental measurements and are not associated with the external excitation. The simulation results verify that the nonlinear changes in measured dynamic FBG responses are due to the progression of damage in the lap joint.

Webb, S.; Shin, P.; Peters, K.; Zikry, M. A.; Stan, N.; Chadderdon, S.; Selfridge, R.; Schultz, S.

2014-02-01

183

Multiplexed adaptive two-wave mixing wavelength demodulation of fiber Bragg grating sensor for monitoring both dynamic and quasi-static drifts  

NASA Astrophysics Data System (ADS)

A multiplexed 4-channel version of two-wave mixing (TWM) wavelength demodulator using InP:Fe photorefractive crystal (PRC) in the C-band (1530-1570nm) is demonstrated. The system can be used as a wavelength demodulator for use with Fiber Bragg Grating (FBG) sensors to monitor both dynamic strains and quasi-static strains. In this configuration, the FBG is illuminated with a broadband source, and any strain in the FBG is encoded as a wavelength shift of the light reflected by the FBG. The reflected light from the FBG is spilt into two unbalanced paths and both beams (pump and signal) mix in the PRC. Any wavelength shift of the reflected light results in an equivalent phase shift between the pump and signal beams as they travel unbalanced path lengths. Since TWM is an adaptive process, the two interfering beams are naturally in quadrature and remain in quadrature even in the presence of large quasi-static strains. In this paper, the demonstrated 4-channel TWM wavelength demodulator is able to demodulate dynamic strains from four FBG sensors simultaneously in the presence of quasi-static drifts. And with the aid of a spectrum analyzer, the quasi-static shifts caused by static strains or temperature changes are obtained by monitoring the spectral shift of the transmitted light through the FBG sensors.

Qiao, Yi; Krishnaswamy, Sridhar

2006-03-01

184

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

185

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

186

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

187

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

188

Bragg grating seismic monitoring system  

NASA Astrophysics Data System (ADS)

A theoretical concept and its experimental realization of a fiber-optic Bragg grating strain sensor system to measure dynamic deformations in rock masses are presented. The system has been designed in order to monitor strain variations in the range of 10-9 within a bandwidth of 0.1 to 2 kHz. First promising results from field experiments are shown where seismic signals have been detected, in comparison with conventional geophone registrations.

Schmidt-Hattenberger, Cornelia; Borm, Gunter; Amberg, F.

1999-12-01

189

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

190

Dipolar distribution generated by laser-induced plasma (LIP) in air in earliest instants  

NASA Astrophysics Data System (ADS)

We present an experimental investigation of the electric field potential and magnetic field generated by a laser-induced plasma in air, for time delays 0 ? t ? 50 ns. The laser used is a Nd?:?YAG, ? = 1064 nm, 10 ns at FWHM, and the irradiance applied is I = (1011-1012) W cm-2. We find that the collective effect of the charges in the plasma form a dynamic dipole distribution aligned with the laser beam axis. This experimental result is explained based on the mobility of the electric charges detected by mapping near the plasma with a coaxial cable probe. Shadowgraphy and fast photography techniques show that the plasma ionization front advances asymmetrically and mostly toward the lens. The intrinsic dipole moment is estimated by applying an external electric field. The magnetic diagnostic shows the presence of a current aligned with the laser beam that gives rise to an azimuthal magnetic field, corroborating the observed dipolar configuration.

Paulin Fuentes, J. Mauricio; Sánchez-Aké, C.; Bredice, Fausto O.; Villagrán-Muniz, Mayo

2013-12-01

191

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

NASA Technical Reports Server (NTRS)

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

Mcdaniel, J. C., Jr.

1982-01-01

192

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

193

Femtosecond-laser-induced destruction of boron-nitride nanotubes and boron-nitride doped graphene  

NASA Astrophysics Data System (ADS)

By means of first principles calculations we studied the intense femtosecond-laser excitation of several boron­ nitride nanotubes and a boron-nitride doped graphene layer up to irradiation levels where these structures disintegrate. We performed molecular dynamics simulations using our in-house Code for Highly excited Valence Electron Systems (CHIVES). For different boron-nitride nanotubes we determined the damage threshold in terms of the electronic temperature and the absorbed energy per atom. We found that all nanotubes studied were destroyed in the first 200 fs after an ultrafast laser excitation heating the electrons to 108 mHa (34103 K). Some tubes also disintegrated at lower electronic temperatures. For the boron-nitride doped graphene we found that at a laser-induced electronic temperature of 100 mHa (31577 K) bonds break and the boron-nitride dimer leaves the structure.

Bauerhenne, Bernd; Eschstruth, Nils; Zijlstra, Eeuwe S.; Garcia, Martin E.

2013-11-01

194

Numerical study of ambient pressure for laser-induced bubble near a rigid boundary  

NASA Astrophysics Data System (ADS)

The dynamics of the laser-induced bubble at different ambient pressures was numerically studied by Finite Volume Method (FVM). The velocity of the bubble wall, the liquid jet velocity at collapse, and the pressure of the water hammer while the liquid jet impacting onto the boundary are found to increase nonlinearly with increasing ambient pressure. The collapse time and the formation time of the liquid jet are found to decrease nonlinearly with increasing ambient pressure. The ratios of the jet formation time to the collapse time, and the displacement of the bubble center to the maximal radius while the jet formation stay invariant when ambient pressure changes. These ratios are independent of ambient pressure.

Li, BeiBei; Zhang, HongChao; Han, Bing; Lu, Jian

2012-07-01

195

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

196

Laser-induced ultrafast demagnetization in ferromagnetic metals.  

PubMed

The laser-induced femtosecond demagnetization in ferromagnetic metals is investigated theoretically. Different from the conventional nanosecond one, this ultrafast demagnetization is a cooperative effect of the external laser field and the internal spin-orbit coupling. The spin-orbit coupling smears out the original identities of triplets and singlets while the laser field uses it as an avenue to influence demagnetization. Importantly, this demagnetization can be manipulated controllably, an essential point to future applications, such as ultrafast control of magneto-optical gating. Finally, the polarization filter effect on the ultrafast time scale is discussed based upon the present theoretical results. PMID:11005994

Zhang, G P; Hübner, W

2000-10-01

197

Laser-Induced Ultrafast Demagnetization in Ferromagnetic Metals  

NASA Astrophysics Data System (ADS)

The laser-induced femtosecond demagnetization in ferromagnetic metals is investigated theoretically. Different from the conventional nanosecond one, this ultrafast demagnetization is a cooperative effect of the external laser field and the internal spin-orbit coupling. The spin-orbit coupling smears out the original identities of triplets and singlets while the laser field uses it as an avenue to influence demagnetization. Importantly, this demagnetization can be manipulated controllably, an essential point to future applications, such as ultrafast control of magneto-optical gating. Finally, the polarization filter effect on the ultrafast time scale is discussed based upon the present theoretical results.

Zhang, G. P.; Hübner, W.

2000-10-01

198

Optimization of confocal laser induced fluorescence in a plasmaa)  

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

199

Femtosecond Visualization of Laser-Induced Optical Relativistic Electron Microbunches  

NASA Astrophysics Data System (ADS)

It has long been known that lasers can interact with relativistic electrons in magnetic undulators to imprint sinusoidal modulations that can be used to slice electrons into microbunches equally separated at the laser wavelength. Here we report on the first direct measurement of laser-induced microbunching of a relativistic electron beam with femtosecond resolution in the time domain. Using a modified zero-phasing technique to map the electron beam's temporal structures into the energy space, we show that this method can be used to directly quantify the time and spectral content of coherent current modulations imprinted on the beam for harmonic and multicolor lasing applications in accelerator-based light sources.

Xiang, Dao; Hemsing, Erik; Dunning, Michael; Hast, Carsten; Raubenheimer, Tor

2014-10-01

200

Characterization of Arcjet Flows Using Laser-Induced Fluorescence  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

201

Communication: Bubbles, crystals, and laser-induced nucleation  

NASA Astrophysics Data System (ADS)

Short intense laser pulses of visible and infrared light can dramatically accelerate crystal nucleation from transparent solutions; previous studies invoke mechanisms that are only applicable for nucleation of ordered phases or high dielectric phases. However, we show that similar laser pulses induce CO2 bubble nucleation in carbonated water. Additionally, in water that is cosupersaturated with argon and glycine, argon bubbles escaping from the water can induce crystal nucleation without a laser. Our findings suggest a possible link between laser-induced nucleation of bubbles and crystals.

Knott, Brandon C.; Larue, Jerry L.; Wodtke, Alec M.; Doherty, Michael F.; Peters, Baron

2011-05-01

202

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

203

Laser induced fluorescence of biochemical for UV LIDAR application.  

PubMed

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

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

2014-05-01

204

Trace metal mapping by laser-induced breakdown spectroscopy  

SciTech Connect

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

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

2012-01-01

205

Laser-induced anisotropy in terbium-gallium garnet  

NASA Astrophysics Data System (ADS)

We observed that a Tb3Ga5O12 crystal when illuminated at the terbium ion resonance, becomes optically uniaxial. The optical axis is found to be along the beam-propagation axis. The origin of this symmetry breakdown is a thermal effect. Our observation of a conoscopic pattern is accounted for by a quadratic stress and refractive index distribution model. By spatial integration of the conoscopic pattern, the laser-induced stress birefringence variation as a function of the incident beam power is determined.

Chen, X.; Gonzalez, S.

1998-11-01

206

Laser-induced anisotropy in terbium-gallium garnet  

Microsoft Academic Search

3  Ga5O12 crystal when illuminated at the terbium ion resonance, becomes optically uniaxial. The optical axis is found to be along\\u000a the beam-propagation axis. The origin of this symmetry breakdown is a thermal effect. Our observation of a conoscopic pattern\\u000a is accounted for by a quadratic stress and refractive index distribution model. By spatial integration of the conoscopic pattern,\\u000a the laser-induced stress birefringence variation

X. Chen; S. Gonzalez

1998-01-01

207

Applications of laser-induced filaments for optical communication links  

NASA Astrophysics Data System (ADS)

Free-space laser communications are subjected to performance degradation when heavy fog or smoke obscures the line of sight (high-loss optical media). On the other hand, it has been demonstrated that laser-induced plasma filaments (LIPF) can propagate for long distances (up to a few kilometers) through clouds and/or turbulent (lossy) atmosphere. Here we propose to use LIPF to improve and/or restore laser communication in adverse, high-loss and/or denied conditions. This work is focused on demonstrating the proof of concept and is dedicated primarily to gaseous, optically transparent media.

Hening, Alexandru; Wayne, David; Lovern, Mike; Lasher, Mark

2014-10-01

208

Velocimetry in gas flows using pulsed laser induced photothermal effects  

NASA Astrophysics Data System (ADS)

The status of theoretical studies and laboratory experiments to apply the laser induced photothermal measurement techniques to diagnose high rate thermal plasma diamond coating deposition performed using an industrial scale induction plasma torch is presented. At the first stage the aim is to measure the plasma flow velocity in the 1000 to 3000 K temperature region near the substrate using the so called time of flight method. The possibility of determining the local concentration of the excited species using the photothermal signals will then be studied.

Vattulainen, J. P.; Hernberg, Rolf G.

209

Search for Laser-Induced Formation of Antihydrogen Atoms  

SciTech Connect

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

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

2006-11-24

210

Evidence of laser induced degradation and graphitization of aromatic pollutants  

NASA Astrophysics Data System (ADS)

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

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

211

Laser-induced fluorescent spectroscopy of steroid hormones  

NASA Astrophysics Data System (ADS)

The laser-induced fluorescence spectra of steroid hormones - estradiol, estriol, estrone, androstenedione - are obtained at excitation of the fourth harmonic of Nd:YAG laser radiation. The quantum yields of fluorescence of these substances were rated by means of the relative method. They are 1.11 X 10-1, 5.20 X 10-3, 8.47 X 10-5. The water solution of tryptophan was used as a standard. The set-up sensitivity for high and average quantum yields substances has been defined.

Samoilova, Elena S.; Fedorov, Vyacheslav I.; Cherkasova, Olga P.; Meshalkin, Yuri P.

2002-07-01

212

Titanium monoxide spectroscopy following laser-induced optical breakdown  

NASA Astrophysics Data System (ADS)

This work investigates Titanium Monoxide (TiO) in ablation-plasma by employing laser-induced breakdown spectroscopy (LIBS) with 1 to 10 TW/cm2 irradiance, pulsed, 13 nanosecond, Q-switched Nd:YAG laser radiation at the fundamental wavelength of 1064 nm. The analysis of TiO is based on our first accurate determination of transition line strengths for selected TiO A-X, B-X, and E-X transitions, particularly TiO A-X ? and B-X ?' bands. Electric dipole line strengths for the A3?-X3? and B3?-X3? bands of TiO are computed. The molecular TiO spectra are observed subsequent to laser-induced breakdown (LIB). We discuss analysis of diatomic molecular spectra that may occur simultaneously with spectra originating from atomic species. Gated detection is applied to investigate the development in time of the emission spectra following LIB. Collected emission spectra allow one to infer micro-plasma parameters such as temperature and electron density. Insight into the state of the micro-plasma is gained by comparing measurements with predictions of atomic and molecular spectra. Nonlinear fitting of recorded and computed diatomic spectra provides the basis for molecular diagnostics, while atomic species may overlap and are simultaneously identified. Molecular diagnostic approaches similar to TiO have been performed for diatomic molecules such as AlO, C2, CN, CH, N2, NH, NO and OH.

Parigger, Christian G.; Woods, Alexander C.; Keszler, Anna; Nemes, László; Hornkohl, James O.

2012-07-01

213

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

214

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

215

Quantitative analysis of ceramics by laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

A quantitative elemental analysis of ceramics was carried out with laser-induced breakdown spectroscopy. A Q-switched Nd:YAG laser was focused on ceramic targets in an argon atmosphere at reduced pressure, and the emission spectra from laser-induced plasma were measured using time-resolved spectroscopy. The experimental results showed that in argon at approximately 200 Torr, the spectral line intensity and the line-to-background ratio were maximized by observing the laser plasma with a time delay of 0.4 ?s. Also, time-resolved measurement of a spectrum in the initial stage of plasma generation (˜1 ?s) was effective for improving the slope of the calibration curve. Based on the results, standard ceramic samples were analyzed for magnesium, aluminum, calcium, iron and titanium, and linear calibration curves with a slope of unity were obtained by measuring spectra with a gate width of 0.4 ?s at a delay time of 0.4 ?s after the laser pulse in argon at 200 Torr.

Kuzuya, M.; Murakami, M.; Maruyama, N.

2003-05-01

216

Laser induced fluorescence imaging system for localization of nasopharyngeal carcinoma  

NASA Astrophysics Data System (ADS)

A laser induced fluorescence imaging system for localization of Nasopharyngeal Carcinoma is developed. In this fluorescence imaging system, the fluorescence intensity with information of detected objection is gained by an image intensifier, which makes color information of the fluorescence image eliminated and the result is a monochrome image of the fluorescence with thermally induced noise. The monochrome fluorescence image is sent to a CCD and captured by an image board, which is controlled by a computer. Image processing is carried out to improve the image quality and therefore improve the system's ability to differentiate carcinomas from normal tissue. Gaussian smoothing is implemented in order to reduce the noise. Image binarizing process is realized to obtain an optimal threshold of the image. Image pixels with grey value below this threshold are assigned as diseased and those above are normal. A pseudo color processing is then accomplished to get better visual perception and understanding of the image, greatly increasing the detail resolution of the grey image. The processed image is then displayed on the screen of the computer in real time. The real time laser induced fluorescence imaging system with the image processing methods developed is efficient for localization of the nasopharyngeal carcinoma.

Liu, Lina; Xie, Shusen

2007-11-01

217

Laser-induced breakdown spectroscopy of tantalum plasma  

SciTech Connect

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

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

2013-07-15

218

Laser induced breakdown spectroscopy library for the Martian environment  

NASA Astrophysics Data System (ADS)

The NASA Mars Science Laboratory rover will carry the first Laser Induced Breakdown Spectroscopy experiment in space: ChemCam. We have developed a laboratory model which mimics ChemCam's main characteristics. We used a set of target samples relevant to Mars geochemistry, and we recorded individual spectra. We propose a data reduction scheme for Laser Induced Breakdown Spectroscopy data incorporating de-noising, continuum removal, and peak fitting. Known effects of the Martian atmosphere are confirmed with our experiment: better Signal-to-Noise Ratio on Mars compared to Earth, narrower peak width, and essentially no self-absorption. The wavelength shift of emission lines from air to Mars pressure is discussed. The National Institute of Standards and Technology vacuum database is used for wavelength calibration and to identify the elemental lines. Our Martian database contains 1336 lines for 32 elements: H, Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl, K, Ar, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Rb, Sr, Cs, Ba, and Pb. It is a subset of the National Institute of Standards and Technology database to be used for Martian geochemistry. Finally, synthetic spectra can be built from the Martian database. Correlation calculations help to distinguish between elements in case of uncertainty. This work is used to create tools and support data for the interpretation of ChemCam results.

Cousin, A.; Forni, O.; Maurice, S.; Gasnault, O.; Fabre, C.; Sautter, V.; Wiens, R. C.; Mazoyer, J.

2011-11-01

219

Estimation of mechanical properties of a viscoelastic medium using a laser-induced microbubble interrogated by an acoustic radiation force n1  

PubMed Central

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

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

2011-01-01

220

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

221

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

222

Biopolymer holographic diffraction gratings  

NASA Astrophysics Data System (ADS)

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

Savi? Ševi?, Svetlana; Panteli?, Dejan

2008-03-01

223

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

224

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

225

Laser-induced decompression shock development in fused silica Junlan Wang,a)  

E-print Network

Laser-induced decompression shock development in fused silica Junlan Wang,a) Richard L. Weaver March 2003 Laser-induced weak shock formation in fused silica is studied using standard wave mechanics comparable to the laser pulse that propagates towards the test film/substrate interface. Reflection

Sottos, Nancy R.

226

Detection of trace Al in model biological tissue with laser-induced breakdown spectroscopy  

E-print Network

Detection of trace Al in model biological tissue with laser-induced breakdown spectroscopy Marian D; accepted 29 May 2007; posted 20 June 2007 (Doc. ID 78984); published 9 August 2007 Laser-induced breakdown was modeled using a 2% agarose gelatin doped with an Al2O3 nanoparticle suspension. A calibration curve

Rehse, Steven J.

227

Escherichia coli identification and strain discrimination using nanosecond laser-induced breakdown spectroscopy  

E-print Network

Escherichia coli identification and strain discrimination using nanosecond laser-induced breakdown April 2007 Three strains of Escherichia coli, one strain of environmental mold, and one strain and E. coli strains. This analysis showed efficient discrimination between laser-induced breakdown

Rehse, Steven J.

228

LASER-INDUCED SHOCK WAVES IN CONDENSED MATTER: SOME TECHNIQUES AND APPLICATIONS  

E-print Network

LASER-INDUCED SHOCK WAVES IN CONDENSED MATTER: SOME TECHNIQUES AND APPLICATIONS S. N. LUOa,Ã? , D. C, NV 89154, USA; c GPS Division, California Institute of Technology, Pasadena, CA 91125, USA Laser pressure physics. We briefly review some techniques in laser-induced shock waves, including direct laser

Asimow, Paul D.

229

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 on one substrate. The design of the proposed thermoelectric generator was selected to demonstrate

230

Neuroprotective therapy for argon-laser-induced retinal injury  

NASA Astrophysics Data System (ADS)

Laser photocoagulation treatment of the central retina is often complicated by an immediate side effect of visual impairment, caused by the unavoidable laser-induced destruction of the normal tissue lying adjacent to the lesion and not affected directly by the laser beam. Furthermore, accidental laser injuries are at present untreatable. A neuroprotective therapy for salvaging the normal tissue might enhance the benefit obtained from treatment and allow safe perifoveal photocoagulation. We have developed a rat model for studying the efficacy of putative neuroprotective compounds in ameliorating laser-induced retinal damage. Four compounds were evaluated: the corticosteroid methylprednisolone, the glutamate-receptor blocker MK-801, the anti-oxidant enzyme superoxide dismutase, and the calcim-overload antagonist flunarizine. The study was carried out in two steps: in the first, the histopathological development of retinal laser injuries was studied. Argon laser lesions were inflicted in the retinas of 18 pigmented rats. The animals were sacrificed after 3, 20 or 60 days and their retinal lesions were evaluated under the light microscope. The laser injury mainly involved the outer layers of the retina, where it destroyed significant numbers of photoreceptor cells. Over time, evidence of two major histopathological processes was observed: traction of adjacent nomral retinal cells into the central area of the lesion forming an internal retinal bulging, and a retinal pigmented epithelial proliferative reaction associated with subretinal neovascularization and invations of the retinal lesion site by phagocytes. The neuroprotective effects of each of the four compounds were verified in a second step of the study. For each drug tested, 12 rats were irradiated wtih argon laser inflictions: six of them received the tested agent while the other six were treated with the corresponding vehicle. Twenty days after laser expsoure, the rats were sacrificed and their lesions were subjected to image-analysis morphometry. The extent of retianl damage was assessed by measuring the lesion diameter and the amount of photoreceptor cell loss in the outer nuclear layer. Methylprednisolone and MI-801 were shown to ameliorate laser-induced retinal damage, whereas both superoxide dismutase and flunarizine were ineffective. Furthermore, MK-801 diminished the proliferative reaction of the retinal pigment epithelial cells. On the basis of our results we suggest that the pigmented rat model is suitable for studying and screening various compounds for their neuroprotective efficacy in treating retinal laser injury. We further suggest that glutamate might play a key role in mediating retinal injury induced by laser irradiation.

Belkin, Michael; Rosner, Mordechai; Solberg, Yoram; Turetz, Yosef

1999-06-01

231

Railway monitoring and train tracking by fiber Bragg grating sensors  

Microsoft Academic Search

The aim of this work is to demonstrate the efficiency of fiber Bragg grating sensors to be used for in situ railway monitoring and train tracking applications. In the specific case, FBGs (Fiber Bragg Gratings) sensors have been bonded to rails in order to perform two different kinds of measurements: dynamic strain to analyze the characteristic frequency response of the

F. Mennella; A. Laudati; M. Esposito; A. Cusano; A. Cutolo; M. Giordano; S. Campopiano; G. Breglio

2007-01-01

232

Thermal Model for Laser-Induced Discharge Surface Strengthening  

NASA Astrophysics Data System (ADS)

The temperature field due to laser-induced discharge surface strengthening (LIDSS) has significant influence on the microstructure transformation and also the formation quality of discharge pit. A transient axisymmetric thermal model is developed to estimate the temperature distribution during LIDSS based on Fourier heat conduction equation. In the model, a Gaussian heat input distribution is assumed; temperature-dependent material properties are applied and the latent heat of fusion and vaporization is calculated on an enthalpy method. As an application, we use this model to compute the temperature field during the process of tungsten tool electrode machining 1045 steel workpiece and find that the computational results are well consistent with the experimental data.

Zhou, Zhongqiang; Wang, Zhitong; Yang, Mingjiang

233

Theoretical model for double pulse laser-induced breakdown spectroscopy.  

PubMed

We present a simple theoretical model for the emission from double pulse laser-induced plasmas that was developed to better understand the processes and factors involved in enhancement of plasma emission. In this model, the plasma emission is directly proportional to the square of plasma density, its volume, and the fraction of second laser pulse absorbed through inverse bremsstrahlung absorption by the plasma plume of the first laser pulse. The electron-ion collision frequency determines the profile and location of the peak of emission enhancement with respect to the delay between the two lasers, whereas the amplitude of the enhancement is mainly dependent on the increase in the mass ablation rate after the second laser pulse. The effects of increase in temperature and in plasma volume after the second laser pulse are also discussed in light of this model. PMID:19122700

Rai, Virendra N; Yueh, Fang Yu; Singh, Jagdish P

2008-11-01

234

Elemental Analysis of Soils by Laser Induced Breakdown Spectroscopy  

NASA Astrophysics Data System (ADS)

The chemical and elemental composition of soil is very complex as it contains many constituents like minerals, organic matters, living organisms, fossils, air and water. Considering the diversity of soil contents, quality and usability, a systematic scientific study on the elemental and chemical composition of soil is very important. In order to study the chemical composition of soil, Laser induced breakdown spectroscopy (LIBS) has been applied recently. The important features of LIBS system and its applications for the measurement of nutrients in green house soil, on-line monitoring of remediation process of chromium polluted soil, determination of trace elements in volcanic erupted soil samples collected from ancient cenozoic lava eruption sites and detection of toxic metals in Gulf war oil spill contaminated soil using LIBS are described in this chapter.

Gondal, Mohammed Ashraf; Dastageer, Mohamed A.

235

Laser-induced ultrafast demagnetization in ferromagnetic metals  

NASA Astrophysics Data System (ADS)

In this talk we will report our latest theoretical study on the laser-induced femtosecond demagnetization in ferromagnetic metals [Ref. Phys. Rev. Lett 85, 3025 (2000)]. It is found that different from the conventional nanosecond one, this ultrafast demagnetization is a cooperative effect of the external laser field and the internal spin-orbit coupling. The spin-orbit coupling smears out the original identities of triplets and singlets while the laser field uses it as an avenue to influence demagnetization. Importantly, this demagnetization can be manipulated controllably, an essential point to future applications, such as ultrafast control of magneto-optical gating. Finally, the polarization filter effect on the ultrafast time scale is discussed based upon the present theoretical results.

Zhang, Guoping; Hübner, Wolfgang

2001-03-01

236

Deep UV laser induced fluorescence in fluoride thin films  

NASA Astrophysics Data System (ADS)

Fluorescence experiments have been performed to study the interaction of 193-nm laser radiation with dielectric thin films of LaF3, AlF3, and MgF2. Spectral- and time-resolved measurements reveal the presence of cerium in LaF3 and the influence of hydrocarbons in MgF2 and LaF3. Virtually no fluorescence response is observable in the case of AlF3. Supplementary measurements on multilayer stacks confirm the contribution of hydrocarbon and cerium emission in high-reflective UV mirrors upon ArF excimer laser irradiation. Energy density dependent measurements indicate a linear absorption process as the origin of UV laser induced fluorescence in LaF3. Luminescence calculations are applied as a helpful tool in order to account for interference effects that are inherently to be found in the multilayer emission spectra.

Heber, J.; Mühlig, C.; Triebel, W.; Danz, N.; Thielsch, R.; Kaiser, N.

237

Quantitative analysis of gallstones using laser-induced breakdown spectroscopy  

SciTech Connect

The utility of laser-induced breakdown spectroscopy (LIBS) for categorizing different types of gallbladder stone has been demonstrated by analyzing their major and minor constituents. LIBS spectra of three types of gallstone have been recorded in the 200-900 nm spectral region. Calcium is found to be the major element in all types of gallbladder stone. The spectrophotometric method has been used to classify the stones. A calibration-free LIBS method has been used for the quantitative analysis of metal elements, and the results have been compared with those obtained from inductively coupled plasma atomic emission spectroscopy (ICP-AES) measurements. The single-shot LIBS spectra from different points on the cross section (in steps of 0.5 mm from one end to the other) of gallstones have also been recorded to study the variation of constituents from the center to the surface. The presence of different metal elements and their possible role in gallstone formation is discussed.

Singh, Vivek K.; Singh, Vinita; Rai, Awadhesh K.; Thakur, Surya N.; Rai, Pradeep K.; Singh, Jagdish P

2008-11-01

238

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

239

Hydrogen retention in tungsten materials studied by Laser Induced Desorption  

NASA Astrophysics Data System (ADS)

Development of methods to characterise the first wall in ITER and future fusion devices without removal of wall tiles is important to support safety assessments for tritium retention and dust production and to understand plasma wall processes in general. Laser based techniques are presently under investigation to provide these requirements, among which Laser Induced Desorption Spectroscopy (LIDS) is proposed to measure the deuterium and tritium load of the plasma facing surfaces by thermal desorption and spectroscopic detection of the desorbed fuel in the edge of the fusion plasma. The method relies on its capability to desorb the hydrogen isotopes in a laser heated spot. The application of LID on bulk tungsten targets exposed to a wide range of deuterium fluxes, fluences and impact energies under different surface temperatures is investigated in this paper. The results are compared with Thermal Desorption Spectrometry (TDS), Nuclear Reaction Analysis (NRA) and a diffusion model.

Zlobinski, M.; Philipps, V.; Schweer, B.; Huber, A.; Reinhart, M.; Möller, S.; Sergienko, G.; Samm, U.; 't Hoen, M. H. J.; Manhard, A.; Schmid, K.; Textor Team

2013-07-01

240

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

241

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

242

Estimating intercellular surface tension by laser-induced cell fusion  

NASA Astrophysics Data System (ADS)

Intercellular surface tension is a key variable in understanding cellular mechanics. However, conventional methods are not well suited for measuring the absolute magnitude of intercellular surface tension because these methods require determination of the effective viscosity of the whole cell, a quantity that is difficult to measure. In this study, we present a novel method for estimating the intercellular surface tension at single-cell resolution. This method exploits the cytoplasmic flow that accompanies laser-induced cell fusion when the pressure difference between cells is large. Because the cytoplasmic viscosity can be measured using well-established technology, this method can be used to estimate the absolute magnitudes of tension. We applied this method to two-cell-stage embryos of the nematode Caenorhabditis elegans and estimated the intercellular surface tension to be in the 30-90 µN m-1 range. Our estimate was in close agreement with cell-medium surface tensions measured at single-cell resolution.

Fujita, Masashi; Onami, Shuichi

2011-12-01

243

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

244

Elemental analysis of slurry samples with laser induced breakdown spectroscopy  

SciTech Connect

Direct analysis of wet slurry samples with laser induced breakdown spectroscopy (LIBS) is challenging due to problems of sedimentation, splashing, and surface turbulence. Also, water can quench the laser plasma and suppress the LIBS signal, resulting in poor sensitivity. The effect of water on LIBS spectra from slurries was investigated. As the water content decreased, the LIBS signal was enhanced and the standard deviation was reduced. To improve LIBS slurry analysis, dried slurry samples prepared by applying slurry on PVC coated slides were evaluated. Univariate and multivariate calibration was performed on the LIBS spectra of the dried slurry samples for elemental analysis of Mg, Si, and Fe. Calibration results show that the dried slurry samples give a good correlation between spectral intensity and elemental concentration.

Eseller, Kemal E.; Tripathi, Markandey M.; Yueh, Fang-Yu; Singh, Jagdish P.

2010-05-01

245

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

246

Containerless study of metal evaporation by laser induced fluorescence  

NASA Technical Reports Server (NTRS)

Laser induced fluorescence (LIF) detection of atomic vapors was used to study evaporation from electromagnetically levitated and CW CO2 laser-heated molybdenum spheres and resistively-heated tungsten filaments. Electromagnetic (EM) levitation in combination with laser heating of tungsten, zirconium, and aluminum specimens was also investigated. LIF intensity vs temperature data were obtained for molybdenum atoms and six electronic states of atomic tungsten, at temperatures up to the melting point of each metal. The detected fraction of the emitted radiation was reduced by self-absorption effects at the higher experimental temperatures. Vaporization enthalpies derived from data for which less than half the LIF intensity was self-absorbed were -636 + or - 24 kJ/g-mol for Mo and 831 + or - 32 kJ/g-mol for W. Space-based applications of EM levitation in combination with radiative heating are discussed.

Schiffman, Robert A.; Nordine, Paul C.

1987-01-01

247

Response of fiber Bragg gratings to longitudinal ultrasonic waves.  

PubMed

In the last years, fiber optic sensors have been widely exploited for several sensing applications, including static and dynamic strain measurements up to acoustic detection. Among these, fiber Bragg grating sensors have been indicated as the ideal candidate for practical structural health monitoring in light of their unique advantages over conventional sensing devices. Although this class of sensors has been successfully tested for static and low-frequency measurements, the identification of sensor performances for high-frequency detection, including acoustic emission and ultrasonic investigations, is required. To this aim, the analysis of feasibilty on the use of fiber Bragg grating sensors as ultrasonic detectors has been carried out. In particular, the response of fiber Bragg gratings subjected to the longitudinal ultrasonic (US) field has been theoretically and numerically investigated. Ultrasonic field interaction has been modeled, taking into account the direct deformation of the grating pitch combined with changes in local refractive index due to the elasto-optic effect. Numerical results, obtained for both uniform and Gaussian-apodized fiber Bragg gratings, show that the grating spectrum is strongly influenced by the US field in terms of shape and central wavelength. In particular, a key parameter affecting the grating response is the ratio between the US wavelength and the grating length. Normal operation characterized by changes in wavelength of undistorted Bragg peak is possible only for US wavelengths longer than the grating length. For US wavelengths approaching the grating length, the wavelength change is accompanied by subpeaks formation and main peak amplitude modulation. This effect can be attributed to the nonuniformity of the US perturbation along the grating length. At very high US frequencies, the grating is not sensitive any longer. The results of this analysis provide useful tools for the design of grating-based ultrasound sensors for meeting specific requirements in terms of field intensity and frequencies. PMID:15801318

Minardo, Aldo; Cusano, Andrea; Bernini, Romeo; Zeni, Luigi; Giordano, Michele

2005-02-01

248

Improved thermal and strain performance of annealed polymer optical fiber Bragg gratings  

Microsoft Academic Search

We report on a detailed study of the inscription and characterization of fiber Bragg gratings (FBGs) in commercial step index polymer optical fibers (POFs). Through the growth dynamics of the gratings, we identify the effect of UV-induced heating during the grating inscription. We found that FBGs in annealed commercial POFs can offer more stable short-term performance at both higher temperature

Wu Yuan; Alessio Stefani; Morten Bache; Torben Jacobsen; Bjarke Rose; Nicolai Herholdt-Rasmussen; Finn Kryger Nielsen; Søren Andresen; Ole Brøsted Sørensen; Knud Styhr Hansen; Ole Bang

2011-01-01

249

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

250

Titanium monoxide spectroscopy following laser-induced optical breakdown  

SciTech Connect

This work investigates Titanium Monoxide (TiO) in ablation-plasma by employing laser-induced breakdown spectroscopy (LIBS) with 1 to 10 TW/cm{sup 2} irradiance, pulsed, 13 nanosecond, Q-switched Nd:YAG laser radiation at the fundamental wavelength of 1064 nm. The analysis of TiO is based on our first accurate determination of transition line strengths for selected TiO A-X, B-X, and E-X transitions, particularly TiO A-X {gamma} and B-X {gamma} Prime bands. Electric dipole line strengths for the A{sup 3}{Phi}-X{sup 3}{delta} and B{sup 3}{Pi}-X{sup 3}{delta} bands of TiO are computed. The molecular TiO spectra are observed subsequent to laser-induced breakdown (LIB). We discuss analysis of diatomic molecular spectra that may occur simultaneously with spectra originating from atomic species. Gated detection is applied to investigate the development in time of the emission spectra following LIB. Collected emission spectra allow one to infer micro-plasma parameters such as temperature and electron density. Insight into the state of the micro-plasma is gained by comparing measurements with predictions of atomic and molecular spectra. Nonlinear fitting of recorded and computed diatomic spectra provides the basis for molecular diagnostics, while atomic species may overlap and are simultaneously identified. Molecular diagnostic approaches similar to TiO have been performed for diatomic molecules such as AlO, C{sub 2}, CN, CH, N{sub 2}, NH, NO and OH.

Parigger, Christian G.; Woods, Alexander C.; Keszler, Anna; Nemes, Laszlo; Hornkohl, James O. [The University of Tennessee/UT Space Institute, Center for Laser Applications, 411 B.H. Goethert Parkway, Tullahoma, TN 37388-9700 (United States); Chemical Research Center of the Hungarian Academy of Sciences, Institute of Materials and Environmental Chemistry, Pusztaszeri ut 59-67, H-1025 Budapest (Hungary); Chemical Research Center of the Hungarian Academy of Sciences, Laser Spectroscopy Laboratory, Pusztaszeri ut 59-67, H-1025 Budapest (Hungary); Hornkohl Consulting, Tullahoma, TN 37388 (United States)

2012-07-30

251

Effects of pulse width on nascent laser-induced bubbles for underwater laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

The reason for the significant advantage offered by long-pulse (150 ns) irradiation in underwater laser-induced breakdown spectroscopy (LIBS) is investigated from the point of view of the behavior of nascent cavitation bubbles. Shadowgraphs of nascent bubbles generated by pulsed laser irradiation of Cu targets in water were observed for two different pulse widths, 20 ns and 150 ns. It is clearly seen that the nascent bubble is formed at the leading edge of the laser pulse profile, regardless of the pulse width. Bubbles generated by a 20-ns pulse are characterized by a flat-shape filled with dense matter with intense optical emission, which is in contrast to more hemispherical low-density bubbles observed under the irradiation by a 150-ns pulse. The behavior of the nascent bubbles is consistent with the behavior of the later plasma in the bubbles, which is crucial for observation of well-defined atomic spectral lines for underwater LIBS.

Sakka, Tetsuo; Tamura, Ayaka; Matsumoto, Ayumu; Fukami, Kazuhiro; Nishi, Naoya; Thornton, Blair

2014-07-01

252

Formation of carbon nanotubes: In situ optical analysis using laser-induced incandescence and laser-induced fluorescence  

NASA Astrophysics Data System (ADS)

Gas-phase production of carbon nanotubes in presence of a metal catalyst with a continuous wave CO2 laser is investigated by combining coherent anti-Stokes Raman scattering (CARS), laser-induced fluorescence (LIF), and laser-induced incandescence (LII). These in situ techniques provide a unique investigation of the different transformation processes of the primarily carbon and metal vapors issued from the vaporization of the target by the laser and the temperature at which these processes occur. Continuous-wave laser provides with stable continuous vaporization conditions very well suited for such in situ investigations. Temperature profiles inside the reactor are known from CARS measurements and flow calculations. Carbon soot, density, and size of carbon aggregates are determined by LII measurements. LIF measurements are used to study the gas phases, namely, C2 and C3 radicals which are the very first steps of carbon recombination, and metal catalysts gas phase. Spectral investigations allow us to discriminate the signal from each species by selecting the correct pair of excitation/detection wavelengths. Spatial distributions of the different species are measured as a function of target composition and temperature. The comparison of LIF and LII signals allow us to correlate the spatial evolution of gas and soot in the scope of the different steps of the nanotube growth already proposed in the literature and to identify the impact of the chemical nature of the catalyst on carbon condensation and nanotube nucleation. Our study presents the first direct evidence of the nanotube onset and that the nucleation proceeds from a dissolution-segregation process from metal particles as assumed in the well-known vapor-liquid-solid model. Comparison of different catalysts reveals that this process is strongly favored when Ni is present.

Cau, M.; Dorval, N.; Attal-Trétout, B.; Cochon, J.-L.; Foutel-Richard, A.; Loiseau, A.; Krüger, V.; Tsurikov, M.; Scott, C. D.

2010-04-01

253

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

254

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

255

Aluminum nitride grating couplers.  

PubMed

Grating couplers in sputtered aluminum nitride, a piezoelectric material with low loss in the C band, are demonstrated. Gratings and a waveguide micromachined on a silicon wafer with 600 nm minimum feature size were defined in a single lithography step without partial etching. Silicon dioxide (SiO(2)) was used for cladding layers. Peak coupling efficiency of -6.6 dB and a 1 dB bandwidth of 60 nm have been measured. This demonstration of wire waveguides and wideband grating couplers in a material that also has piezoelectric and elasto-optic properties will enable new functions for integrated photonics and optomechanics. PMID:22695653

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

2012-06-10

256

Numerical Modelling of Biomass Grate Furnaces  

Microsoft Academic Search

Computational Fluid Dynamics (CFD) is increasingly being used for the optimisation of industrial coal furnaces and gas burners. Due to the high complexity of heterogeneous combustion of fixed or moving biomass fuel beds, only few research projects have so far dealt with the introduction of CFD as a cost-efficient tool in the optimisation of biomass grate furnaces. The present work

Robert Scharler; Ingwald Obernberger

2000-01-01

257

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

PubMed

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

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

2013-11-01

258

Semiconductor laser asymmetry cutting glass with laser induced thermal-crack propagation  

NASA Astrophysics Data System (ADS)

Laser induced thermal-crack propagation (LITP) makes the material to produce an uneven temperature field, maximum temperature can't soften or melt the material, induces the thermal stress, then the crack separates along the cutting path. One of the problems in laser asymmetry cutting glass with LITP is the cutting deviation along scanning trajectory. This study lays great emphasis on considering the dynamic extension of crack to explain the reason of the cutting deviation in laser asymmetry cutting glass, includes asymmetric linear cutting and a quarter of a circular curve cutting. This paper indicates the experiments of semiconductor laser asymmetry cutting glass with LITP. Optical microscope photographs of the glass sheet are obtained to examine the cutting deviation. The extended finite element method (XFEM) is used to simulate the dynamic propagation of crack; the crack path does not have to be specified a priori. The cutting deviation mechanism and the crack propagation process are studied by the stress fields using finite element software ABAQUS. This work provides a theoretical basis to investigate the cutting deviation in laser asymmetry cutting glass. In semiconductor laser asymmetry cutting glass, the tensile stress is the basis of crack propagation, then the compressive stress not only makes the crack to extend stably, but also controls the direction of crack propagation.

Zhao, Chunyang; Zhang, Hongzhi; Wang, Yang

2014-12-01

259

Hard X-ray emission in laser-induced vacuum discharge  

NASA Astrophysics Data System (ADS)

The dynamics of fast laser-induced vacuum discharge, with a rather small value of amplitude of current ([less-than-or-equal] 10 kA), as well as the voltage and energy of the capacitor bank ([less-than-or-equal] 20 kV and 20 J, respectively), have been investigated. It has been experimentally demonstrated that the initiations conditions determined by the energy and duration of the laser radiation, fundamentally determine the dynamics of the discharge. Two types of space and time separated plasma instabilities are revealed. It was found that the first of instabilities occurs at the initial stage of the discharge and is caused by a pinch structure, which takes place in front of a cathode jet extending in vacuum. The second type of instabilities arises at the top or recession of the current and is accompanied by the generation of hard (energy [greater-than-or-equal]100 keV) bremsstrahlung X-ray radiation from the anode area. The excess energy of the hard components of radiation over the potential of the current source is associated with the effects of plasma-erosive breaking.

Korobkin, Yu. V.; Romanov, I. V.; Rupasov, A. A.; Shikanov, A. S.; Gupta, P. D.; Khan, R. A.; Kumbhare, S. R.; Moorti, A.; Naik, P. A.

2005-09-01

260

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

261

Subwavelength gratings and applications  

NASA Astrophysics Data System (ADS)

This Ph. D thesis investigates the fabrication and applications of subwavelength gratings. The first objective of this study is aimed at finding low-cost, high throughput fabrication techniques that are capable of producing high-quality nano-scale gratings over a relatively large scale. The second objective is to explore the applications of nano-scale gratings in subwavelength optical elements (SOE), a new type of compact, highly efficient optical devices that are compatible with semiconductor device fabrication technologies and have the potential to be suitable for integration. This thesis is divided into 5 chapters. Chapter 1 is an introduction to the subject of gratings. A brief review of the evolution of different grating fabrication methods and applications is included in this chapter. Chapters 2, 3, and Chapter 4 of the thesis are devoted to the question of nano-scale grating fabrication. Technologies concerning the generation of high spatial-frequency periodic patterns over a large scale using interference lithography (IL) are covered in Chapter 2. The role of nanoimprint lithography (NIL) as a low-cost replication tool for the production of nano-gratings is discussed in detail in Chapters 3 and 4. More specifically: Chapter 3 presents several NIL-based technologies that are used to overcome some of the limitations inherent with the interference lithography fabrication process; Chapter 4 presents a novel mask technology promising for the large-scale production of gratings by NIL. Finally, several applications of nano-scale gratings in subwavelength optical elements (SOE) are discussed in Chapter 5. Most of the SOE devices investigated in this study are based on the birefringence and the index-averaging effects of nano-gratings in the long-wavelength domain. A brief summary of the general theory 103--104 proposed by P.Yeh et al. concerning the optical properties of subwavelength gratings can be found in Appendix A. Since the orientation-dependent wet chemical etching of silicon was used extensively in this research, a relatively detailed discussion of this technique is also included in Appendix B of this dissertation.

Yu, Zhaoning

262

Bulk and surface structural properties of Si 1- x- yGe xC y layers processed on Si(001) by pulsed laser induced epitaxy  

NASA Astrophysics Data System (ADS)

Si 1- x- yGe xC y films have been grown by pulsed laser induced epitaxy (PLIE) from C + implanted pseudomorphic Si 1- xGe x films and from hydrogenated amorphous a-SiGeC:H films deposited on Si(001). The laser treated samples are examined by electron channelling patterns analysis, X-ray diffraction, channelling Rutherford backscattering spectroscopy and atomic force microscopy (AFM). If laser fluence exceeds a threshold for which the melted zone is thicker than the initial SiGeC layer, the laser induced epitaxy is effective. We show that laser fluence strongly influences germanium profiles. Germanium and carbon atoms are redistributed over the melted depth with a graded profile. Strain profiles, deduced from X-ray dynamical diffraction simulations, exhibit the same gradual evolution from the surface down to the substrate. AFM measurements show a strong decrease of rugosity obtained with suitable PLIE operating conditions.

Guedj, C.; Boulmer, J.; Bouchier, D.; Clerc, C.; Calvarin, G.; Godet, C.; Roca i Cabarrocas, P.; Houze, F.; Mencaraglia, D.

1996-08-01

263

Color separation gratings  

NASA Technical Reports Server (NTRS)

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

Farn, Michael W.; Knowlden, Robert E.

1993-01-01

264

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

265

Analysis of human nails by laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) is applied to analyze human fingernails using nanosecond laser pulses. Measurements on 45 nail samples are carried out and 14 key species are identified. The elements detected with the present system are: Al, C, Ca, Fe, H, K, Mg, N, Na, O, Si, Sr, Ti as well as CN molecule. Sixty three emission lines have been identified in the spectrum that are dominated by calcium lines. A discriminant function analysis is used to discriminate among different genders and age groups. This analysis demonstrates efficient discrimination among these groups. The mean concentration of each element is compared between different groups. Correlation between concentrations of elements in fingernails is calculated. A strong correlation is found between sodium and potassium while calcium and magnesium levels are inversely correlated. A case report on high levels of sodium and potassium in patients with hyperthyroidism is presented. It is shown that LIBS could be a promising technique for the analysis of nails and therefore identification of health problems.

Hosseinimakarem, Zahra; Tavassoli, Seyed Hassan

2011-05-01

266

Laser-induced fluorescence for discrimination of crops and weeds  

NASA Astrophysics Data System (ADS)

This paper reports the use of Laser Induced Fluorescence (LIF) of plants to discriminate between crops and weeds for potential use in an intelligent crop spraying system. Past and current work in intelligent crop spraying has concentrated on using multi-spectral reflectance data in particular using near infrared (NIR) and color. Texture and shape image processing has also been used with limited success and is usually computationally expensive. Also, most of these approaches are error prone since they rely on ambient solar illumination and so are susceptible to errors caused by cloud variations, shadows and other non-uniformities. There are several commercial spraying systems available that detect presence or absence of plants using the NIR 'red-edge' effect without discrimination between species. 'Weedseeker' and 'Detectspray' are two examples of such systems, the 'Weedseeker' system being one of the few active systems, incorporating its own light source. However, both systems suffer from poor spatial resolution. The use of plant or chlorophyll fluorescence for discrimination between species is a relatively under researched area. This paper shows that LIF of several crops and weeds can be used to discriminate between species. Spectra are presented for two crop and two weed species over a range of discrete laser excitation wavelengths. The technique can be directly implemented with a laser imaging system for real-time detection and discrimination of crops and weeds.

Hilton, Peter J.

2000-11-01

267

Laser-induced fluorescence in the detection of esophageal carcinoma  

NASA Astrophysics Data System (ADS)

Laser induced fluorescence (LIF) is a technique which can perform an 'optical biopsy' of gastrointestinal mucosa. LIF was performed in resected specimens using a pulsed N2-laser coupled fiberoptically to a probe. Fluorescence was measured using a 0.2 meter spectroscope with an intensified photodiode array. Measurements were made on fresh (<30 minutes after resection) esophageal specimens containing normal mucosa, Barrett's esophagus, and adenocarcinoma. Each tissue section was examined using an optical probe consisting of a central fiber for delivering the excitation energy and a 6 fiber bundle surrounding the central fiber for detection of the fluorescence. An excitation wavelength of 337 nm was used which generated 3-ns pulses while fluorescence intensities were acquired from 300-800 nm. Spectra were obtained from each section in a standardized fashion and background spectra subtracted. Fluorescence readings were taken from 54 normal esophageal sections and 32 sections of adenocarcinoma. A fluorescence index obtained from the tumor sections was 0.68+/- 0.01 compared with 0.51+/- 0.01 for the normal sections (p<0.001). Using a discriminant value of 0.65, this technique had a sensitivity of 81% and a specificity of 100% for detection of malignant tissue. The positive predictive value was 100% and the negative predictive value was 90% for an overall accuracy of 93%. LIF is a promising technique which has the capability of distinguishing normal versus malignant tissue in the esophagus with good accuracy.

Wang, Kenneth K.; Gutta, Kumar; Laukka, Mark A.; Densmore, John

1995-01-01

268

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

269

Effects of laser prepulses on laser-induced proton generation  

NASA Astrophysics Data System (ADS)

Low-intensity laser prepulses (<1013 W cm-2, nanosecond duration) are a major issue in experiments on laser-induced generation of protons, often limiting the performances of proton sources produced by high-intensity lasers (?1019 W cm-2, picosecond or femtosecond duration). Depending on the intensity regime, several effects may be associated with the prepulse, some of which are discussed in this paper: (i) destruction of thin foil targets by the shock generated by the laser prepulse; (ii) creation of preplasma on the target front side affecting laser absorption; (iii) deformation of the target rear side; and (iv) whole displacement of thin foil targets affecting the focusing condition. In particular, we show that under oblique high-intensity irradiation and for low prepulse intensities, the proton beam is directed away from the target normal. Deviation is towards the laser forward direction, with an angle that increases with the level and duration of the ASE pedestal. Also, for a given laser pulse, the beam deviation increases with proton energy. The observations are discussed in terms of target normal sheath acceleration, in combination with a laser-controllable shock wave locally deforming the target surface.

Batani, D.; Jafer, R.; Veltcheva, M.; Dezulian, R.; Lundh, O.; Lindau, F.; Persson, A.; Osvay, K.; Wahlström, C.-G.; Carroll, D. C.; McKenna, P.; Flacco, A.; Malka, V.

2010-04-01

270

Laser-Induced Breakdown Spectroscopy of Cinematographic Film  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) was used to characterize the composition of black-and-white, silver-gelatine photographic films. LIB spectra of samples and reference gelatine (of various gel strengths, Bloom values 225 and 75 and crosslinking degrees) were acquired in vacuum by excitation at 266 nm. The elemental composition of the gelatine used in the upper protective layer and in the underlying emulsion is revealed by the stratigraphic analysis carried out by delivering successive pulses on the same spot of the sample. Silver (Ag) lines from the light-sensitive silver halide salts are accompanied by iron, lead and chrome lines. Fe and Pb are constituents of film developers and Cr is included in the hardening agent. The results demonstrate the analytical capacity of LIBS for study and classification of different gelatine types and the sensitivity of the technique to minor changes in gelatine composition. In addition LIBS analysis allows extracting important information on the chemicals used as developers and hardeners of archival cinematographic films.

Oujja, M.; Abrusci, C.; Gaspard, S.; Rebollar, E.; Amo, A. del; Catalina, F.; Castillejo, M.

271

Femtosecond laser induced nanostructuring for surface enhanced Raman spectroscopy  

NASA Astrophysics Data System (ADS)

The formation of periodical nanostructures with femtosecond laser pulses was used to create highly efficient substrates for surface-enhanced Raman spectroscopy (SERS). We report about the structuring of silver and copper substrates and their application to the SERS of DNA (herring sperm) and protein molecules (egg albumen). The maximum enhancement factors were found on Ag substrates processed with the second harmonic generation (SHG) of a 1-kHz Ti:sapphire laser and structure periods near the SHG wavelength. In the case of copper, however, the highest enhancement was obtained with long-period ripples induced with at fundamental wavelength. This is explained by an additional significant influence of nanoparticles on the surface. Nanostructured areas in the range of 1.25 mm2 were obtained in 10 s. The surfaces were characterized by scanning electron microscopy, Fast Fourier Transform and Raman spectroscopy. Moreover, the role of the chemical modification of the metal structures is addressed. Thin oxide layers resulting from working in atmosphere which improve the biocompatibility were indicated by vibration spectra. It is expected that the detailed study of the mechanisms of laser-induced nanostructure formation will stimulate further applications of functionalized surfaces like photocatalysis, selective chemistry and nano-biology.

Messaoudi, H.; Das, S. K.; Lange, J.; Heinrich, F.; Schrader, S.; Frohme, M.; Grunwald, R.

2014-03-01

272

Laser induced formation of micro-rough structures  

NASA Astrophysics Data System (ADS)

Laser induced micro-rough structures (LIMS) are a by-product of laser ablation process and are created during multiple pulse irradiation on the surface of the material. Although LIMS have been found to be deleterious for the thin film deposition process, these surfaces have wide variety of applications in synthesis of adherent coatings in thermal expansion mismatched systems. Earlier models, based on interference effects of the laser beam, to explain the evolution of LIMS, are not consistent with the experimental results. Experiments were conducted on a wide variety of materials (e.g. SiC, alumina, YBaCuO superconductor, etc.) to understand the mechanisms for generation of the micro-rough structures. A novel model was developed to explain the characteristics of LIMS such as (i) feature orientation (ii) evolution of surface structures as a function of pulses, (iii) formation of LIMS within a energy window near ablation threshold and (iv) periodicity which is independent of the laser wavelength and incident angle.

Singh, Rajiv K.; Fitz-Gerald, James M.

1997-01-01

273

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

274

Environmental application of pulsed laser-induced incandescence  

NASA Astrophysics Data System (ADS)

A portable instrument based on two-color laser-induced incandescence (LII) technique has been designed and developed for the detection of carbonaceous particles for environmental applications. The instrument has been calibrated by performing LII measurements at the exhaust of a home-made soot generator. The incandescence signal from particles sampled into the instrument has been compared with in situ, calibrated, LII measurements to correlate the incandescence signal by the instrument with particles concentration. Measurements of particulate with the LII instrument were then conducted in different environmental conditions, covering a wide range of concentration (from ambient air to cars’ exhaust). The detection limit of the LII instrument has been estimated to be in the range of 200 ng/m3. These measurements have been also compared with results obtained with a commercial aethalometer. The results show a linear relationship between the two sets of measurements, also in the case where significant variation of the carbon particles concentration has been observed over time. These observations allow us to infer that the two instruments are responding in the same way to different carbon particles load, size and nature.

Migliorini, Francesca; De Iuliis, Silvana; Maffi, Silvia; Zizak, Giorgio

2013-09-01

275

Future Development for Laser-Induced Thermal Acoustics  

NASA Astrophysics Data System (ADS)

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

Schlamp, Stefan

2002-07-01

276

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

277

Wavelet-based laser-induced ultrasonic inspection in pipes  

NASA Astrophysics Data System (ADS)

The feasibility of detecting localized defects in tubing using Wavelet based laser-induced ultrasonic-guided waves as an inspection method is examined. Ultrasonic guided waves initiated and propagating in hollow cylinders (pipes and/or tubes) are studied as an alternative, robust nondestructive in situ inspection method. Contrary to other traditional methods for pipe inspection, in which contact transducers (electromagnetic, piezoelectric) and/or coupling media (submersion liquids) are used, this method is characterized by its non-contact nature. This characteristic is particularly important in applications involving Nondestructive Evaluation (NDE) of materials because the signal being detected corresponds only to the induced wave. Cylindrical guided waves are generated using a Q-switched Nd:YAG laser and a Fiber Tip Interferometry (FTI) system is used to acquire the waves. Guided wave experimental techniques are developed for the measurement of phase velocities to determine elastic properties of the material and the location and geometry of flaws including inclusions, voids, and cracks in hollow cylinders. As compared to the traditional bulk wave methods, the use of guided waves offers several important potential advantages. Some of which includes better inspection efficiency, the applicability to in-situ tube inspection, and fewer evaluation fluctuations with increased reliability.

Baltazar-López, Martín E.; Suh, Steve; Chona, Ravinder; Burger, Christian P.

2006-02-01

278

Picosecond laser induced periodic surface structure on copper thin films  

NASA Astrophysics Data System (ADS)

LIPSS (Laser Induced Periodic Surface Structure) formation on copper thin films induced by a picosecond laser beam (Nd:YAG laser at 266 nm, 42 ps and 10 Hz) was studied experimentally. Copper thin films were deposited on glass and silicon substrates by magnetron sputtering. The surface modifications of irradiated zones were analyzed by scanning electron microscopy. Two distinct types of LIPSS were identified with respect to the laser fluence (F), number of laser shots (N) and substrate material. Namely, with a number of laser shots (1000 < N < 10,000) and a fluence of (200 mJ/cm2 < F < 500 mJ/cm2), Low Spatial Frequency LIPSS (LSFL with a spatial period of ? ? 260 nm and an orientation perpendicular to polarization) and High Spatial Frequency LIPSS (HSFL with a spatial period of ? ? 130 nm and an orientation parallel to the polarization) were observed. The regime of regular spikes formation was determined for N ? 1000. Moreover, the 2D-map of the relationship among LIPSS formation, laser fluence and number of laser shots on copper thin film with two different substrates was established. A physics interpretation of regular spikes and LIPSS formation on copper thin film induced by ps laser with overlapping multi-shots is proposed based on experimental data and the theory of Plateau-Rayleigh instability.

Huynh, Thi Trang Dai; Petit, Agnès; Semmar, Nadjib

2014-05-01

279

Seedless Laser Velocimetry Using Heterodyne Laser-Induced Thermal Acoustics  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

280

Laser-induced fluorescence temperature measurements in natural convection flowfields  

SciTech Connect

Planar laser-induced iodine fluorescence temperature measurements are presented in natural convection flowfields. The technique can be used to make spatially-resolved measurements in complex three-dimensional flowfields. The flowfield measured consists of a cubic enclosure, 8 inches on a side, with a one inch heated cube sitting on the bottom surface of the enclosure. An additional measurement is made where a glass plate is placed above the heated cube to divert the plume and makes the flowfield considerably more complex. The side and bottom walls of the enclosure are made of glass and the top wall is made of aluminum and is held at a constant temperature close to room temperature. A laser sheet is passed through a plane at the center of the flowfield. A fluorescence image, from trace amounts of iodine vapor introduced into the test cell, is collected with a cooled CCD camera. For the uniform seeding fraction, uniform absolute pressure conditions present in the test cell, the fluorescence intensities are functions only of the local temperature of the flow. The image intensities are scaled using a theoretical model of the fluorescence. For the tests presented here temperatures ranged from 20 to 150 C although the technique could be applied to significantly higher temperature conditions. The accuracy is estimated to be 4 C.

Donohue, J.M.

1997-07-01

281

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

282

Systems for creation of laser-induced damage images and problems of their optimization  

NASA Astrophysics Data System (ADS)

Creation of laser-induced damage imags inside transparent materials is one of the technical and art applications of laser induced damage phenomena. The purpose of the paper is to present the laser induced damage image technology and to discus problems of the optimization of the system producing the images. At the beginning a brief historical overview and patent situation are presented. An exemplary block-diagram of laser etching system for simultaneous production of several images inside several articles is shown and some peculiarities due to specific formation of laser induced micro-damages are discussed. Several methods for generating 3D images and portraits allowing reproduction of them within an optically transparent materials with the same resolution like computer processed images, without sharp to point structure and without significant fluctuations of gray shades are disclosed. Technique of image reproduction without undesirable regular arrangement of etch points is presented.

Troitski, Igor N.

2000-03-01

283

NON-CONTACT MICROSCALE MANIPULATION USING LASER-INDUCED CONVECTION FLOWS  

E-print Network

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.2 Natural convection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2NON-CONTACT MICROSCALE MANIPULATION USING LASER-INDUCED CONVECTION FLOWS TH`ESE pr´esent´ee `a L.3 Thermocapillary convection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.3.1 Surface tension

Boyer, Edmond

284

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...

285

Laser-Induced Breakdown Spectroscopy as a Tool to Differentiate Compositions of Iron-Bearing Minerals  

NASA Astrophysics Data System (ADS)

This study demonstrates that laser-induced breakdown spectroscopy onboard the MSL Curiosity rover can be used to differentiate various classes of iron-rich minerals on Mars using principle component analysis of specific elemental peaks.

Rosen-Gooding, A. L.; Ollila, A. M.; Gordon, S. R.; Newsom, H. E.; Williams, A. J.; Martinez, R. K.; Wiens, R. C.; Clegg, S. M.

2014-07-01

286

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

287

Time-resolved studies of Nd:YAG laser-induced breakdown. Plasma formation, acoustic wave generation, and cavitation.  

PubMed

The use of high intensity ultrashort pulsed laser radiation to produce optical breakdown is an important approach for the surgical treatment of intraocular structures. We have investigated the transient properties of Nd:YAG laser induced breakdown in a saline model using time-resolved spectroscopic techniques. Spatially resolved pump and probe techniques are applied to study the dynamic behavior of the plasma formation, acoustic wave generation, and cavitation processes which accompany the optical breakdown. Measurements of plasma shielding and luminescence indicate that the laser induced plasma forms on a subnanosecond time scale and has a lifetime of several nanoseconds. An acoustic transient is generated at the breakdown site and propagates spherically outward with an initial hypersonic velocity, then loses energy and propagates at sound velocity. Transient heating following the plasma formation produces a liquid-gas phase change and gives rise to cavitation or gas bubble formation. This gas bubble expands rapidly for several microseconds, then slows to reach its maximum size and finally collapses. PMID:4066213

Fujimoto, J G; Lin, W Z; Ippen, E P; Puliafito, C A; Steinert, R F

1985-12-01

288

Laser-induced radical generation and evolution to a self-sustaining flame  

Microsoft Academic Search

Images and emission spectra of sparks produced by laser-induced breakdown of methane and propane air mixtures were investigated with a high degree of spatial and temporal resolution. The laser-induced breakdown was generated by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser. The data were collected using an intensified high-speed camera and a single\\/multi-fiber Cassegrain optics system coupled to

J. L. Beduneau; N. Kawahara; T. Nakayama; E. Tomita; Y. Ikeda

2009-01-01

289

Microscopic and spectroscopic imaging of laser-induced forward transfer and its application to material transfer  

Microsoft Academic Search

As an investigation of the process of laser-induced forward transfer (LIFT), the behaviors of atoms, thermally radiating hot droplets and comparatively cold droplets were observed by two-dimensional laser-induced fluorescence (2D-LIF), laser light scattering (LLS) and thermal radiation. The observations were done with different parameters such as ablation laser energy, film thickness and gas pressure. The condition for the deposition of

Yoshiki Nakata; Tatsuo Okada; Mitsuo Maeda

2004-01-01

290

Use of fiber optic guided, laser induced acoustic waves for nde  

E-print Network

USE OF FIBER OPTIC GUIDED, LASER INDUCED ACOUSTIC WAVES FOR NDE A Thesis by CHARLES EDWARD DUFFER Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER... OF SCIENCE December 1990 Major Subject: Mechanical Engineering USE OF FIBER OPTIC GUIDED, LASER INDUCED ACOUSTIC WAVES FOR NDE A Thesis by CHARLES EDWARD DUFFER Approved as to style and content by: Christian P. Burger (Chair of Committee) Peter...

Duffer, Charles Edward

2012-06-07

291

Laser-induced periodic annular surface structures on fused silica surface  

SciTech Connect

We report on the formation of laser-induced periodic annular surface structures on fused silica irradiated with multiple femtosecond laser pulses. This surface morphology emerges after the disappearance of the conventional laser induced periodic surface structures, under successive laser pulse irradiation. It is independent of the laser polarization and universally observed for different focusing geometries. We interpret its formation in terms of the interference between the reflected laser field on the surface of the damage crater and the incident laser pulse.

Liu, Yi; Brelet, Yohann; Forestier, Benjamin; Houard, Aurelien [Laboratoire d'Optique Appliquee, ENSTA/CNRS/Ecole Polytechnique, 828, Boulevard des Marechaux, Palaiseau F-91762 (France)] [Laboratoire d'Optique Appliquee, ENSTA/CNRS/Ecole Polytechnique, 828, Boulevard des Marechaux, Palaiseau F-91762 (France); He, Zhanbing [Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, Antwerp B-2020 (Belgium)] [Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, Antwerp B-2020 (Belgium); Yu, Linwei [Laboratoire de Physique des Interfaces et des Couches Minces, Ecole Polytechnique, CNRS, Palaiseau F-91128 (France)] [Laboratoire de Physique des Interfaces et des Couches Minces, Ecole Polytechnique, CNRS, Palaiseau F-91128 (France); Deng, Yongkai; Jiang, Hongbing [Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871 (China)] [Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871 (China)

2013-06-24

292

Laser induced forward transfer of SnO2 for sensing applications using different precursors systems  

NASA Astrophysics Data System (ADS)

This paper presents the transfer of SnO2 by laser induced forward transfer (LIFT) for gas sensor applications. Different donor substrates of SnO2 with and without triazene polymer (TP) as a dynamic release layer were prepared. Transferring these films under different conditions were evaluated by optical microscopy and functionality. Transfers of sputtered SnO2 films do not lead to satisfactory results and transfers of SnO2 nanoparticles are difficult. Transfers of SnO2 nanoparticles can only be achieved when applying a second laser pulse to the already transferred material, which improves the adhesion resulting in a complete pixel. A new approach of decomposing the transfer material during LIFT transfer was developed. Donor films based on UV absorbing metal complex precursors namely, SnCl2(acac)2 were prepared and transferred using the LIFT technique. Transfer conditions were optimized for the different systems, which were deposited onto sensor-like microstructures. The conductivity of the transferred material at temperatures of about 400 ?C are in a range usable for SnO2 gas sensors. First sensing tests were carried out and the transferred material proved to change conductivity when exposed to ethanol, acetone, and methane.

Mattle, Thomas; Hintennach, Andreas; Lippert, Thomas; Wokaun, Alexander

2013-02-01

293

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

294

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

295

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

296

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

297

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

PubMed

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 ~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. PMID:21743529

Nath, Arpita; Khare, Alika

2011-07-01

298

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

299

Paper-based colorimetric enzyme linked immunosorbent assay fabricated by laser induced forward transfer.  

PubMed

We report the Laser Induced Forward Transfer (LIFT) of antibodies from a liquid donor film onto paper receivers for application as point-of-care diagnostic sensors. To minimise the loss of functionality of the active biomolecules during transfer, a dynamic release layer was employed to shield the biomaterial from direct exposure to the pulsed laser source. Cellulose paper was chosen as the ideal receiver because of its inherent bio-compatibility, liquid transport properties, wide availability and low cost, all of which make it an efficient and suitable platform for point-of-care diagnostic sensors. Both enzyme-tagged and untagged IgG antibodies were LIFT-printed and their functionality was confirmed via a colorimetric enzyme-linked immunosorbent assay. Localisation of the printed antibodies was exhibited, which can allow the creation of complex 2-d patterns such as QR codes or letters for use in a final working device. Finally, a calibration curve was determined that related the intensity of the colour obtained to the concentration of active antibodies to enable quantitative assessment of the device performance. The motivation for this work was to implement a laser-based procedure for manufacturing low-cost, point-of-care diagnostic devices on paper. PMID:24926392

Katis, Ioannis N; Holloway, Judith A; Madsen, Jens; Faust, Saul N; Garbis, Spiros D; Smith, Peter J S; Voegeli, David; Bader, Dan L; Eason, Robert W; Sones, Collin L

2014-05-01

300

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

301

Laser-induced circular nanostructures in fused silica assisted by a self-assembling chromium layer  

NASA Astrophysics Data System (ADS)

Nanostructures have a widespread field of applications and are of growing industrial importance. However, the economic fabrication of nanostructures poses a critical challenge. In this work, a fundamental research of a laser-induced surface nanostructuring of fused silica using the dynamic self-assembling structure formation in metal layers is presented. This method may offer promising opportunities for nanostructuring of dielectrics. This new approach is demonstrated by the formation of randomly distributed concentric nanostructures into fused silica. The irradiation of chromium-covered fused silica samples with a KrF excimer laser results in melting, partial ablation, restructuring, and resolidification of both the metal layer and the dielectric surface. In this way, concentric circular structures into the dielectric were formed with dimensions that can be controlled by the laser fluence ? and by the pulse number N. The distance of the concentric rings increases with increasing laser fluence. The experimental results were compared with simulated structure dimensions taking into account the heat equation and the Navier-Stokes equation. Despite the currently applied decoupled approach for the simulations, i.e. separating the heat equation and the fluid flow, a good agreement of simulation results with experimental data was achieved.

Lorenz, Pierre; Klöppel, Michael; Frost, Frank; Ehrhardt, Martin; Zimmer, Klaus; Li, Pu

2013-09-01

302

Assessment of laser-induced release of drugs from liposomes: An in vitro study  

SciTech Connect

We evaluated the characteristics of laser-induced release of an antimetabolite (cytosine arabinoside) from temperature-sensitive liposomes. Previous work had shown that a laser would induce breakdown of liposomes when a dye was encapsulated within the liposomes. The present investigation was performed to determine if release could be induced from liposomes that did not contain dye. In vitro, dynamic studies of the release of the drug from liposomes diluted in blood (flowing in a capillary tube at 40 microns/min) were conducted using an argon dye laser operating either in the blue-green mode (488/514 nm) or in the dye mode (577 nm). A radio-labeled marker was used to monitor the drug release. The results showed that the drug could indeed be released from liposomes that did not contain dye, at energy levels that are not likely to be harmful to the tissue. At identical power levels, the release of the drug was greater at 577 nm than at 488/514 nm, probably owing to the greater light absorbance of hemoglobin at the longer wavelength. The results indicate the potential for the site-specific release of a variety of molecules in the ocular vasculature.

Khoobehi, B.; Char, C.A.; Peyman, G.A. (Louisiana State Univ. Medical Center School of Medicine, New Orleans (USA))

1990-01-01

303

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

304

Remote laser-induced breakdown spectroscopy (LIBS) for lunar exploration  

NASA Astrophysics Data System (ADS)

Laser-induced breakdown spectroscopy (LIBS) is an active analytical technique that makes use of a laser pulse to analyze materials of interest at a distance by creating a plasma, which emits photons at characteristic emission line wavelengths. We validate the technique for planetary exploration under vacuum conditions. We review the capability and advantages of the LIBS technique for lunar regolith analysis at 1.5 m distance from a lunar rover, and we characterize its potential for the detection of resources for future exploration, such as the determination of regolith water content. The limits of detection determined for the major elements (typically <1 wt %) help to determine regolith parent material such as feldspathic highland rocks, rocks from the ancient magmatic high magnesian suite (Mg-suite), Fe-rich mare basalts or potassium, rare earth element, and phosphorus-rich (KREEP-rich) samples. Compositional parameters commonly used to classify lunar regoliths such as TiO2, Al2O3, and K2O abundances are readily determined by LIBS. Certain elements support regolith analysis: For example, Ba and Zr can be used to confirm KREEP-like composition, while quantifying the Ni and Co content can be used to infer the amount of meteoritic material. Finally, it is shown that the ice content of lunar soil produces strong H emissions with the LIBS techniques at the 25 wt % H2O level, while measurements on altered basalts give a limit of detection of about 1 wt % for H2O content. This demonstrates that the 5.6 wt % water content detected by the recent LCROSS experiment should be easily detectable and quantifiable by LIBS analysis.

Lasue, J.; Wiens, R. C.; Clegg, S. M.; Vaniman, D. T.; Joy, K. H.; Humphries, S.; Mezzacappa, A.; Melikechi, N.; McInroy, R. E.; Bender, S.

2012-01-01

305

Characterization of cinematographic films by Laser Induced Breakdown Spectroscopy  

NASA Astrophysics Data System (ADS)

The emulsion-coated transparent plastic-base film has been the main carrier for production and preservation of motion picture contents since the 19th century. The knowledge of the composition of black and white silver gelatine cinematographic films is of great importance for the characterization of the photographic process and for identifying the optimum conditions for conservation. A cinematographic film is a multi-component system that consists of a layer of photographic emulsion overcoating a polymeric support (plasticized cellulose triacetate) and a protective transparent cross-linked gelatine layer coating the emulsion. In the present work, Laser Induced Breakdown Spectroscopy (LIBS) is used to characterize the composition of the materials of cinematographic films. LIB spectra of film samples and of different individual film components, polymeric support and reference gelatines, were acquired in vacuum by excitation at 266 nm (Q-switched Nd:YAG laser, 6 ns, 10 Hz). In the cinematographic film, silver lines from the light-sensitive silver halide salts of the photographic emulsion are accompanied by iron, lead, chrome and phosphorus lines. Iron and lead are constituents of film developers, chrome is included in the composition of the hardening agents and phosphorus has its origin in the plasticizer used in the polymeric support. By applying successive pulses on the same spot of the film sample, it was possible to observe through stratigraphic analysis the different layers composition. Additionally, the results obtained reveal the analytical capacity of LIBS for the study and classification of the different gelatine types and qualities used for the protecting layer and the photographic emulsion.

Gaspard, S.; Oujja, M.; Rebollar, E.; Abrusci, C.; Catalina, F.; Castillejo, M.

2007-12-01

306

Laser-induced breakdown spectroscopy based deminers' probe  

NASA Astrophysics Data System (ADS)

We report on a prototype Laser Induced Breakdown Spectroscopy (LIBS) Deminers' Probe used to identify underground objects. We have built a prototype, and are in the process of developing a more advanced LIBS based Deminer' s Probe used to prod objects underground, and then sense them by creating a micro-plasma plume of the surface material and analyzing the spectrum of the emitted light to identify the object. It is expected that the Deminer will be able to eliminate many false positives, which consume most of the Deminers' time. SARA Fiber-Optics coupled LIBS system consists in a probe that can be inserted into the ground to provide a path for both the laser beam to the target, and for the micro-plasma plume fluorescence from the target to a spectrometer or spectrometers for analysis. The probe is closely modeled after the conventional Deminers' probe, resembling a saber. We have demonstrated that this simple system is capable of producing remarkably different spectra from different materials. Our next steps are to add a number of features to the Deminers' Probe. These include: a new optical configuration to increase the irradiance and fluence created by the pulsed laser at the target, a multiple channel fluorescence reception system that can increase the amount of light delivered to the spectrometers, a fluidic system to clear the detritus away from the probe tip, and a complete operational/control and readout system for the Deminer to use. Mine-lane tests are planned to be performed in the later part of 2009, or shortly thereafter.

Hauck, James P.; Walker, Mark; Hamadani, Siavosh; Bloomhardt, Natalie; Eagan, Justin

2009-05-01

307

Fiber Bragg grating sensor and waveguide grating sensor  

Microsoft Academic Search

Several new designes of different type fiber Bragg grating(FBG) sensors, including long range strain sensor, pressure sensor, and displacement sensor, have been introduced. A new concept of sliced fiber Bragg grating as free space optical element has been presented. Some new waveguide Bragg grating writing technologies have been introduced.

Pin Long

2011-01-01

308

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

309

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

310

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

311

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

312

Application of underwater shock wave and laser-induced liquid jet to neurosurgery  

NASA Astrophysics Data System (ADS)

Paper deals with applications of underwater shock waves to medicine. A historical development of underwater shock wave generation by using pulsed Ho:YAG laser beam irradiation in water is briefly described and an overview is given regarding potential applications of shock waves to neuro-surgery. The laser beam irradiation in a liquid-filled catheter produces water vapor bubble and shock waves intermittently produces micro-liquid jets in a controlled fashion from the exit of the catheter. Correlations between shock dynamics and bubble dynamics are emphasized. To optimize the jet motion, results of basic parametric studies are briefly presented. The liquid jet discharged from the catheter exit has an impulse high enough to clearly exhibit effectiveness for various medical purposes. In liquid jets we observed reasonably strong shock waves and hence invented a compact shock generator aiming to apply to microsurgery. We applied it to a rat's bone window and developed an effective method of brain protection against shock loading. The insertion of Gore-Tex® sheet is found to attenuate shock waves drastically even for very short stand off distance and its physical mechanism is clarified. The laser-induced liquid jet (LILJ) is successfully applied to soft tissue dissection. Animal experiments were performed and results of histological observations are presented in details. Results of animal experiments revealed that LILJ can sharply dissect soft tissue with a minimum amount of liquid consumption, while blood vessels larger than 0.2 mm in diameter are preserved. Shock waves and LILJ have a potential to be indispensable tools in neuro-surgery.

Tominaga, T.; Nakagawa, A.; Hirano, T.; Sato, J.; Kato, K.; Hosseini, S. H. R.; Takayama, K.

2006-03-01

313

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

314

Direct visualization of secretion from single bovine adrenal chromaffin cells by laser-induced native fluorescence imaging microscopy  

SciTech Connect

Direct visualization of the secretion process of individual bovine adrenal chromaffin cells was achieved with laser-induced native fluorescence imaging microscopy. By monitoring the native fluorescence of catecholamines excited by the 275 nm laser line with an intensified charge-coupled-device (CCD) camera, we obtained good temporal and spatial resolution simultaneously without using additional fluorescent probes. Large variations were found among individual cells in terms of the amounts of catecholamines secreted and the rates of secretion. Different regions of a cell also behave differently during the secretion process. However, the degree of this local heterogeneity is smaller than in neurons and neuralgia. The influence of deep-ultraviolet (UV) laser excitation on cells is also discussed. This quantitative imaging technique provides a useful noninvasive approach for the study of dynamic cellular changes and the understanding of the molecular mechanisms of secretory processes. {copyright} {ital 1998} {ital Society for Applied Spectroscopy}

Tong, W.; Yeung, E.S. [Ames Laboratory---USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)] [Ames Laboratory---USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 50011 (United States)

1998-03-01

315

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

316

Application of femtosecond-laser induced nanostructures in optical memory.  

PubMed

The femtosecond laser induced micro- and nanostructures for the application to the three-dimensional optical data storage are investigated. We have observed the increase of refractive index due to local densification and atomic defect generation, and demonstrated the real time observation of photothermal effect after the femtosecond laser irradiation inside a glass by the transient lens (TrL) method. The TrL signal showed a damped oscillation with about an 800 ps period. The essential feature of the oscillation can be reproduced by the pressure wave creation and propagation to the outward direction from the irradiated region. The simulation based on elastodynamics has shown that a large thermoelastic stress is relaxed by the generation of the pressure wave. In the case of soda-lime glass, the velocity of the pressure wave is almost same as the longitudinal sound velocity at room temperature (5.8 microm/ns). We have also observed the localized photo-reduction of Sm3+ to Sm2+ inside a transparent and colorless Sm(3+)-doped borate glass. Photoluminescence spectra showed that some the Sm3+ ions in the focal spot within the glass sample were reduced to Sm2+ ions after femtosecond laser irradiation. A photo-reduction bit of 200 nm in three-dimensions can be recorded with a femtosecond laser and readout clearly by detecting the fluorescence excited by Ar+ laser (lambda = 488 nm). A photo-reduction bit can be also erased by photo-oxidation with a cw Ar+ laser (lambda = 514.5 nm). Since photo-reduction bits can be spaced 150 nm apart in a layer within glass, a memory capacity of as high as 1 Tbit can be achieved in a glass piece with dimensions of 10 mm x 10 mm x 1 mm. We have also demonstrated the first observation of the polarization-dependent periodic nanostructure formation by the interference between femtosecond laser light and electron acoustic waves. The observed nanostructures are the smallest embedded structures ever created by light. The period of self-organized nanostructures can be controlled from approximately 140 to 320 nm by the pulse energy and the number of irradiated pulses. Furthermore, we have also observed the self-assembled sub-wavelength periodic structures created in silica glass by femtosecond pulses on the plane of the propagation of light. PMID:17455477

Shimotsuma, Yasuhiko; Sakakura, Masaaki; Miura, Kiyotaka; Qiu, Jiarong; Kazansky, Peter G; Fujita, Koji; Hirao, Kazuyuki

2007-01-01

317

Excimer Laser Induced Electrical Conductivity and Nanostructures in Polymers.  

NASA Astrophysics Data System (ADS)

The generation of substantial electrical conductivity in high temperature polymers and thin film C_ {60} by means of KrF (248 nm) excimer laser irradiation has been investigated. Formation of both laser ablated surface structures and laser induced electrically conducting wires in polymers with nanometer dimensions is also demonstrated. The electrical conductivity of polymers has been changed by up to 18 orders of magnitude by laser irradiation, obtaining values exceeding 10 Omega^ {-1} cm^{-1} . The conducting material consists of graphitized carbon clusters whose size varies from 2-50 nm. The conduction mechanism is phonon assisted variable range hopping. The large change in the electrical conductivity is an example of a three dimensional percolative metal-insulator phase transition. The critical volume fraction is determined to be Phi_{rm c} = 0.30 +/- 0.05 and the critical exponent is t = 2.2 +/- 0.4. The electrical conductivity of thin film C _{60} has been altered by more than seven orders of magnitude with laser irradiation, obtaining values of 1 Omega^{ -1} cm^{-1}. The threshold for KrF laser ablation of C_{60 } is determined to be 20 +/- 2 mJ/cm^2.. Modification of the surface morphology and the electrical conductivity of polymers with high spatial resolution using excimer lasers has also been achieved. Using holographic techniques with a KrF excimer laser, periodic lines structures with periods ranging from 166 nm to 950 nm were ablated into polyimide (Kapton^{rm TM }) and polybenzimidazole (PBI). The nonlinear nature of laser ablation permits linewidths as small as 30 nm to be obtained, exceeding the resolution expected from linear optics. These experiments establish a new spatial resolution limit for laser ablation and illustrate the dependence of resolution on material properties. This technique was combined with the ability to modify the electrical conductivity of polymers to produce an array of permanently electrically conducting wires in polyimide with a 0.5 ?m width and a 0.9 mu m period. The electrical conductivity of these submicron wires exceeded 1 Omega^ {-1} cm^{-1}. .

Phillips, Harvey Monroe

318

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

319

Quantitative Remote Laser-Induced Breakdown Spectroscopy by Multivariate Analysis  

NASA Astrophysics Data System (ADS)

The ChemCam instrument selected for the Mars Science Laboratory (MSL) rover includes a remote Laser- Induced Breakdown Spectrometer (LIBS) that will quantitatively probe samples up to 9m from the rover mast. LIBS is fundamentally an elemental analysis technique. LIBS involves focusing a Nd:YAG laser operating at 1064 nm onto the surface of the sample. The laser ablates material from the surface, generating an expanding plasma containing electronically excited ions, atoms, and small molecules. As these electronically excited species relax back to the ground state, they emit light at wavelengths characteristic of the species present in the sample. Some of this emission is directed into one of three dispersive spectrometers. In this paper, we studied a suite of 18 igneous and highly-metamorphosed samples from a wide variety of parageneses for which chemical analyses by XRF were already available. Rocks were chosen to represent a range of chemical composition from basalt to rhyolite, thus providing significant variations in all of the major element contents (Si, Fe, Al, Ca, Na, K, O, Ti, Mg, and Mn). These samples were probed at a 9m standoff distance under experimental conditions that are similar to ChemCam. Extracting quantitative elemental concentrations from LIBS spectra is complicated by the chemical matrix effects. Conventional methods for obtaining quantitative chemical data from LIBS analyses are compared with new multivariate analysis (MVA) techniques that appear to compensate for these chemical matrix effects. The traditional analyses use specific elemental peak heights or areas, which compared with calibration curves for each element at one or more emission lines for a series of standard samples. Because of matrix effects, the calibration standards generally must have similar chemistries to the unknown samples, and thus this conventional approach imposes severe limitations on application of the technique to remote analyses. In this suite of samples, the use of traditional methods results in chemical analyses with significant uncertainties. Alternatively, greatly-improved quantitative elemental analysis was accomplished by using a Partial Least Squares (PLS) calibration model for all of the major elements of interest. Principal Components Analysis (PCA) and Soft Independent Modeling of Class Analogy (SIMCA) are then employed to predict the rock-type of the sample. These MVA techniques appear to compensate for these matrix effects because the analysis finds correlations between the spectra (independent variables), the individual elements of interest (dependent variables such as Si) as well as the other elements in the matrix.

Clegg, S. M.; Sklute, E. C.; Dyar, M. D.; Barefield, J. E.; Wiens, R. C.

2007-12-01

320

Fabrication of higher order Bragg gratings in microstructured polymer fibers  

NASA Astrophysics Data System (ADS)

We present the experimental investigations of the Bragg gratings writing process in the microstructured polymer fiber using UV beam of 325 nm wavelength and standard phase mask technique. The good quality higher order peaks placed at ?B/2=782 nm and 2?B/3=1040 nm for the grating with primary peak at ?B=1555 nm were experimentally demonstrated for the first time. The growth dynamics for all the peaks was investigated.

Statkiewicz-Barabach, G.; Kowal, D.; Mergo, P.; Urbanczyk, W.

2013-05-01

321

Generation and expansion of laser-induced plasma as a spectroscopic emission source  

NASA Astrophysics Data System (ADS)

Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spectrochemical analysis for example with laser-induced breakdown spectroscopy (LIBS) has become so popular that one tends to forget the complex physical and chemical processes leading to its generation and governing its evolution. The purpose of this review article is to summarize the backgrounds necessary to understand and describe the laser-induced plasma from its generation to its expansion into the ambient gas. The objective is not to go into the details of each process; there are numerous specialized papers and books for that in the literature. The goal here is to gather in a same paper the essential understanding elements needed to describe laser-induced plasma as results from a complex process. These elements can be dispersed in several related but independent fields such as laser-matter interaction, laser ablation of material, optical and thermodynamic properties of hot and ionized gas, or plasma propagation in a background gas. We believe that presenting the ensemble of understanding elements of laser-induced plasma in a comprehensive way and in limited pages of this paper will be helpful for further development and optimized use of the LIBS technique. Experimental results obtained in our laboratory are used to illustrate the studied physical processes each time such illustration becomes possible and helpful.

Yu, Jin; Ma, Qianli; Motto-Ros, Vincent; Lei, Wenqi; Wang, Xiaochun; Bai, Xueshi

2012-12-01

322

A holographic grating study on a crystal-to-crystal photodimerization and thermal backreaction  

NASA Astrophysics Data System (ADS)

The thermally reversible single-crystal-to-single-crystal [2+2] photodimerization of a styrylpyrylium salt, (E)-2,6-Di-tert-butyl-4-[2-(4-methoxyphenyl)-ethenyl]pyrylium- trifluormethansulfonate, has been investigated by means of a laser-induced holographic grating technique. By irradiation far into the long wavelength absorption tail, the single crystalline character of the sample can be retained both during the photodimerization and the thermal backreaction. Without irradiation the holographic gratings are stable at room temperature, but decay at elevated temperatures. From the temperature dependence of the holographic growth and decay curves an upper limit for the activation energy for the photodimerization is obtained to 15.2 kJ/mol. For the thermal cyclobutane cleavage an activation energy of 99 kJ/mol and an attempt frequency of 1.2×1012 s-1 are found.

Köhler, W.; Novak, K.; Enkelmann, V.

1994-12-01

323

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

324

Imaging monitoring techniques applications in the transient gratings detection  

NASA Astrophysics Data System (ADS)

Experimental studies of Degenerate four-wave mixing (DFWM) in iodine vapor at atmospheric pressure and 0? and 25? are reported. The Laser-induced grating (LIG) studies are carried out by generating the thermal grating using a pulsed, narrow bandwidth, dye laser .A new image processing system for detecting forward DFWM spectroscopy on iodine vapor is reported. This system is composed of CCD camera, imaging processing card and the related software. With the help of the detecting system, phase matching can be easily achieved in the optical arrangement by crossing the two pumps and the probe as diagonals linking opposite corners of a rectangular box ,and providing a way to position the PhotoMultiplier Tube (PMT) . Also it is practical to know the effect of the pointing stability on the optical path by monitoring facula changing with the laser beam pointing and disturbs of the environment. Finally the effects of Photostability of dye laser on the ration of signal to noise in DFWM using forward geometries have been investigated in iodine vapor. This system makes it feasible that the potential application of FG-DFWM is used as a diagnostic tool in combustion research and environment monitoring.

Zhao, Qing-ming

2009-07-01

325

The manufacture of a binary optic liquid crystal blazed grating and its electro-optical properties  

NASA Astrophysics Data System (ADS)

A photoresist film was applied on the indium tin oxide (ITO) conductive glass which was coated with silver. The photoinduced changes of the photoresist film were achieved by exposure to UV lamp through a grating & lead pattern photomask. The photoresist film exhibited grating lines and lead patterns after development. The Ag-ITO double film coated with photoresist patterns was etched to double-layer electrode patterns by ion beam. After photoresists were stripped, silver grating electrodes were removed and ITO grating electrodes were coated with polyimide (PI) and treated by rubbing. The orientation was perpendicular to grating. The back electrode was a piece of ITO glass which was oriented by the same method. Nematic liquid crystal (LC) was injected into the grating cell. Other silver-leads were retained and connected with driver ICs and flex circuits. The binary optic liquid crystal blazed grating was fabricated. Step-shaped phase was obtained by applying a step-shaped voltage on LC grating electrodes. It formed blazed grating at one order and the diffraction angle can be shifted dynamically. The sample was checked up by the optical microscope and the He-Ne laser. The results indicate that the sample had clear grating structure and every grating electrode can be controlled separately. The range of the first order of diffraction angle was +/-6° in theory. The diffraction efficiency decreased as the diffraction angle increased, and the maximum diffraction efficiency can exceed 80 %.

Liu, Kun; Huang, Ziqiang; Wang, Jimin; Wu, Zhiyong; Sun, Yangdong; Kong, Lingjiang

2010-10-01

326

Laser-induced acoustic desorption (LIAD) mass spectrometry.  

PubMed

Large thermally labile molecules were not amenable to mass spectrometric analysis until the development of atmospheric pressure evaporation/ionization methods, such as electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI), since attempts to evaporate these molecules by heating induces degradation of the sample. While ESI and MALDI are relatively soft desorption/ionization techniques, they are both limited to preferential ionization of acidic and basic analytes. This limitation has been the driving force for the development of other soft desorption/ionization techniques. One such method employs laser-induced acoustic desorption (LIAD) to evaporate neutral sample molecules into mass spectrometers. LIAD utilizes acoustic waves generated by a laser pulse in a thin metal foil. The acoustic waves travel through the foil and cause desorption of neutral molecules that have been deposited on the opposite side of the foil. One of the advantages of LIAD is that it desorbs low-energy molecules that can be ionized by a variety of methods, thus allowing the analysis of large molecules that are not amenable to ESI and MALDI. This review covers the generation of acoustic waves in foils via a laser pulse, the parameters affecting the generation of acoustic waves, possible mechanisms for desorption of neutral molecules, as well as the various uses of LIAD by mass spectrometrists. The conditions used to generate acoustic or stress waves in solid materials consist of three regimes: thermal, ablative, and constrained. Each regime is discussed, in addition to the mechanisms that lead to the ablation of the metal from the foil and generation of acoustic waves for two of the regimes. Previously proposed desorption mechanisms for LIAD are presented along with the flaws associated with some of them. Various experimental parameters, such as the exact characteristics of the laser pulse and foil used, are discussed. The internal and kinetic energy of the neutral desorbed molecules are also considered. Our research group has been instrumental in the development and use of LIAD. For example, we have systematically examined the influence of many parameters, such as the type of the foil and its thickness, as well as the analyte layer's thickness, on the efficiency of desorption of neutral molecules. The coupling of LIAD with different instruments and ionization techniques allows for broad use of LIAD in our research laboratories. The most important applications involve analytes that cannot be analyzed by using other mass spectrometric methods, such as large saturated hydrocarbons and heavy hydrocarbon fractions of petroleum. We also use LIAD to characterize lipids, peptides, and oligonucleotides. Fundamental research on the reactions of charged mono-, bi-, and polyradicals with biopolymers, especially oligonucleotides, also requires the use of LIAD, as well as thermochemical measurements for neutral biopolymers. These are but a few of the uses of LIAD in our research group. PMID:22641723

Dow, Alex M; Wittrig, Ashley R; Kenttämaa, Hilkka I

2012-01-01

327

[Measurement of fruit maturity based on laser-induced photoluminescence spectrum].  

PubMed

Grounding on the concepts of biophotonics measurement, the authors first used a red semiconductor laser (655 nm) to irradiate fruits. Compared with other kinds of illuminating sources, the red semiconductor laser is less expensive and takes little space. The laser-induced photoluminescence spectrums could be detected by coupling fibre-optics probe when the fruits are illuminated by laser. And the spectrum has a distinct peak of relative intensity around the 685 nm wavelength that varies with the degree of fruit maturity. Sugar content measurement was used to prove the laser-induced photoluminescence measurement. The authors tested the sugar content of the fruit specimens, and found that the relative peak value of the fruits' laser-induced photoluminescence spectrum decreases with the increase in their sugar content. The authors used partial least-squares (PLS) regression to perform an analysis of the relationship between the laser-induced photoluminescence intensity and the sugar content, fitting a curve of the two parameters. The correlation coefficient r of the fitted value and the actual value is 98.92% for red-inside plum and 97.31% for nectarine. So the authors could generalize that there is an approximate linear relationship between the peak value of laser-induced photoluminescence intensity and the sugar content of fruits, and we could use the maturity measurement based on this concept to decide the fruit ripeness. The authors designed the analytic program for this laser-induced photoluminescence spectrum measurement system, which mainly realizes two functions: generating the standard ripe spectrum of a certain kind of fruit from a quantity of their spectra, and, according to this standard spectrum, determining the maturity degree of an unknown spectrum, and at the same time, displaying the unknown laser-induced photoluminescence spectrum. Incorporating this analytic program with the optical spectrometer, it becomes conceivable to test the fruit maturity very conveniently and quickly. The measurement system of fruit maturity based on laser-induced photoluminescence spectrum has also been used to test various fruits. This measurement is nondestructive and inexpensive, and does not require complicated equipment, a feature of great importance in real-time measurement of fruit maturity. PMID:19248480

Wang, Le-yan; Zhang, Dong-xian; Zhang, Hai-jun; Wang, Xiao-ping

2008-12-01

328

On-Demand Patterning of Indium Tin Oxide Microdots by Laser-Induced Dot Transfer  

NASA Astrophysics Data System (ADS)

Laser-induced dot transfer is an innovative micropatterning technique that realizes on-demand microdot deposition under room-temperature atmospheric conditions. Based on this method, we have developed site- and size-controlled micropatterning of oxide materials. As a model case, indium tin oxide (ITO) microdots were arrayed on a receiver substrate. A nanosecond, 266 nm laser pulse was focused onto the interface between the ITO film and transparent support, causing the ejection of a single ITO microdroplet. The dependence of the transferred structures on the film thickness as well as the laser-induced film temperature distribution has been investigated by both experimental and finite elemental approaches.

Narazaki, Aiko; Kurosaki, Ryozo; Sato, Tadatake; Niino, Hiroyuki

2013-09-01

329

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

330

Laser-induced lensing effects in solid-state optical refrigerators  

NASA Astrophysics Data System (ADS)

Laser-induced thermal and population lensing effects in solid-state optical refrigerator materials are quantitatively evaluated. Time-resolved lensing transients in Yb3+ doped ZBLAN and aluminosilicate glasses are measured, and the model decouples thermal and population lensing effects. The analysis yields the net power density, the cooling efficiency, and important photo-physical parameters. The respective values are in good agreement with previously reported parameters for ZBLAN glass. Aluminosilicate glass is found to be a promising optical refrigerator material. We show that the measurement of laser-induced lensing is a valuable tool that can advance the characterization and optimization of materials for cryogenic optical refrigerators.

Silva, J. R.; Andrade, L. H. C.; Lima, S. M.; Hehlen, M. P.; Guyot, Y.; Medina, A. N.; Malacarne, L. C.; Baesso, M. L.; Astrath, N. G. C.

2013-04-01

331

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

332

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

NASA Astrophysics Data System (ADS)

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.

2008-09-01

333

Laser-Induced Acoustic Desorption Coupled with a Linear Quadrupole Ion Trap Mass Spectrometer  

PubMed Central

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 Finnigan LTQ mass spectrometer. The LQIT was modified for a LIAD probe by outfitting the removable back plate of the instrument with a 6” 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 higher intrinsic sensitivity of the LQIT resulted in a net higher sensitivity relative to the FT-ICR. PMID:20000769

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

2009-01-01

334

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; Huttmann, Gereon; von Smolinski, Dorthe; Gebert, Andreas

2007-01-01

335

Mechanisms of laser-induced dissection and transport of histologic specimens.  

PubMed

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 mum 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 microm 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

2007-12-15

336

Time-domain laser-induced fluorescence spectroscopy apparatus for clinical diagnostics  

NASA Astrophysics Data System (ADS)

We report the design and development of a compact optical fiber-based apparatus for in situ time-resolved laser-induced fluorescence spectroscopy (tr-LIFS) of biological systems. The apparatus is modular, optically robust, and compatible with the clinical environment. It incorporates a dual output imaging spectrograph, a gated multichannel plate photomultiplier (MCP-PMT), an intensified charge-coupled-device (ICCD) camera, and a fast digitizer. It can accommodate various types of light sources and optical fiber probes for selective excitation and remote light delivery/collection as required by different applications. The apparatus allows direct recording of the entire fluorescence decay with high sensitivity (nM range fluorescein dye concentration with signal-to-noise ratio of 46) and with four decades dynamic range. It is capable of resolving a broad range of fluorescence lifetimes from hundreds of picoseconds (as low as 300 ps) using the MCP-PMT coupled to the digitizer to milliseconds using the ICCD. The data acquisition and analysis process is fully automated, enabling fast recording of fluorescence intensity decay across the entire emission spectrum (0.8 s per wavelength or ˜40 s for a 200 nm wavelength range at 5 nm increments). The spectral and temporal responses of the apparatus were calibrated and its performance was validated using fluorescence lifetime standard dyes (Rhodamin B, 9-cyanoanthracene, and rose Bengal) and tissue endogenous fluorophores (elastin, collagen, nicotinamide adenine dinucleotide, and flavin adenine dinucleotide). Fluorescence decay lifetimes and emission spectra of all tested compounds measured with the current tr-LIFS apparatus were found in good agreement with the values reported in the literature. The design and performance of tr-LIFS apparatus have enabled in vivo studies of atherosclerotic plaques and brain tumors.

Fang, Qiyin; Papaioannou, Thanassis; Jo, Javier A.; Vaitha, Russel; Shastry, Kumar; Marcu, Laura

2004-01-01

337

Development of brain tumor demarcation technique using two-color laser-induced fluorescence  

NASA Astrophysics Data System (ADS)

In the field of neurosurgery for brain tumor, it is crucially important to remove almost totally certain brain tumors because of patients' quality of life. However, there has been few effective means of determining the boundaries between tumor tissue and surrounding normal brain parenchyma, making tumor resection totally dependent on the experiencing judgment of surgeons. Therefore, it is quite desirable to construct a real-time and highly sensitive monitoring system to detect tumor margins during surgery. In this study, proposed is the novel photo-dynamic diagnosis method for glioma-surgery. Using excited fluorescence from an oncotropic luminophore dye generally used in PDT and auto-fluorescence from some intracellular enzymes, e.g. NADH (Reduced Nicotinamide Adenine Dinucleotide), the ratio-metric technique in two-color laser-induced fluorescence was experimentally applied to brain tumor detection. The experiment was conducted using brain tumor rat models. An oncotoropic fluorescent dye, NPe6 (mono-L-aspartyl chlorin e6), was injected intravenously and then two fluorescence images were taken with irradiation of violet light, The fluorescence intensities of intracellular enzymes and NPe6 were found to decrease and increase in tumor lesions, respectively. Fluorescence intensity ratio could quantitatively identify tumor margins. Undesirable fluorescence variation could be reduced, which was dependent on inhomogeneous irradiation intensity distribution due to brain surface shape and illuminating light source itself. Thus, the ratio image could achieve higher contrast enhancement in tumor boundaries than single-color PDD. Furthermore, the histological examination provided correlation with ratio-image enhanced area. Consequently, the present method was clarified to be effective to brain tumor monitoring and quantitative tumor boundary demarcation.

Matsumoto, Maki; Saeki, Souichi; Kajiwara, Koji; Ishihara, Hideyuki; Amano, Takayuki; Nishizaki, Takafumi; Saito, Takashi; Suzuki, Michiyasu

2005-11-01

338

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

339

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

340

Index grating lifetime in photorefractive GaAs  

NASA Technical Reports Server (NTRS)

The index grating lifetime in liquid encapsulated Czochralski-grown undoped semi-insulating GaAs was measured using a beam coupling technique. The largest lifetime measure was about 8 s under a read beam intensity of 0.7 mW/sq cm with the grating periodicity being 0.63 microns. The measured value decreases to milliseconds as the read beam intensity and the grating periodicity increase to about 10 mW/sq cm and 4 microns, respectively. This range of grating lifetime in this material is adequate for its use in real-time spatial light modulators, reconfigurable beam steering devices, and dynamic memory elements, for optical computing. In addition, the results suggest that the lifetime is sensitive to residual imperfections in the crystal.

Cheng, Li-Jen; Partovi, Afshin

1988-01-01

341

Investigation of helium addition for laser-induced plasma spectroscopy of pure gas phase systems: Analyte interactions and signal enhancement  

E-print Network

Investigation of helium addition for laser-induced plasma spectroscopy of pure gas phase systems in plasma properties, namely electron density and laser- plasma coupling. Helium addition is concluded breakdown processes. © 2007 Elsevier B.V. All rights reserved. Keywords: LIBS; Laser-induced plasma

Hahn, David W.

342

Laser-Induced Breakdown Spectroscopy: A Novel Technology for the Rapid Detection, Identification, and Discrimination of Biological Agents  

E-print Network

nanosecond laser-induced breakdown spectroscopy," accepted for publication, Applied Physics Letters, MarchLaser-Induced Breakdown Spectroscopy: A Novel Technology for the Rapid Detection, Identification Palchaudhuri2 1Department of Physics and Astronomy and 2Department of Immunology and Microbiology, Wayne State

Rehse, Steven J.

343

Grating-structured metallic microsprings.  

PubMed

We fabricate grating-structured metallic microsprings with well-defined helical angles and diameters, which are self-rolled from strained nanomembranes patterned with gratings. The grating structures on the metal membrane, replicated from the imprinted polymer layer beneath, give rise to the controlled rolling direction after selective etching of the underlying sacrificial layer. The rolling direction of the grating-structured thin metal film is always perpendicular to the long side edge of gratings, offering a good way to roll up strained strips into well controlled three-dimensional (3D) microsprings simply by altering the dimension and orientation of the structured strips. The mechanical elasticity of these grating-structured metallic microsprings is verified for the potential application as a flow rate sensor. Our work may stimulate rigorous synthesis of highly functional and complex 3D helical micro and nanostructures, and hint a broad range of applications such as environmental sensors, micro-/nanoscale robots, metamaterials, etc. PMID:24728100

Huang, Tao; Liu, Zhaoqian; Huang, Gaoshan; Liu, Ran; Mei, Yongfeng

2014-08-21

344

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

345

Holographic grating formation in photopolymers  

NASA Astrophysics Data System (ADS)

We introduce a model describing real-time grating formation in holographic photopolymers, assuming that the diffusion of free monomers is much faster than the grating formation. This model, which combines polymerization kinetics with results from coupled-wave theory, indicates that the grating formation time depends sublinearly on the average holographic recording intensity and the beam intensity ratio controls the grating index modulation at saturation. We validate the model by comparing its predictions with the results of experiments in which DuPont HRF-150X001 photopolymer was used.

Piazzolla, Sabino; Jenkins, B. Keith

1996-07-01

346

Highly efficient accelerator of dense matter using laser-induced cavity pressure acceleration  

E-print Network

Highly efficient accelerator of dense matter using laser-induced cavity pressure acceleration J-rays generated by a guided laser wakefield accelerator inside capillary tubes Appl. Phys. Lett. 100, 191106 (2012) 2D particle-in-cell simulations of ion acceleration in laser irradiated submicron clusters including

Liska, Richard

347

Quantitative rescattering theory for laser-induced high-energy plateau photoelectron spectra Zhangjin Chen,1  

E-print Network

Quantitative rescattering theory for laser-induced high-energy plateau photoelectron spectra- proximation. We further show that experimental photoelectron spectra for a wide range of laser intensity be extracted from experimental photoelectron spectra. By generalizing the QRS theory to molecular targets, we

Lin, Chii-Dong

348

[Study of enhancement effect of laser-induced crater on plasma radiation].  

PubMed

Single pulses exported from high-energy neodymium glass laser were used to act on the same position of soil sample surface repeatedly, and the plasma emission spectra generated from sequential laser pulse action were collected by spectral recording system. The experimental results show that the laser-induced soil plasma radiation was enhanced continuously under the confinement effect of the crater walls, and the line intensities and signal-to-background ratios both had different improvements along with increasing the number of acting pulses. The photographs of the plasma image and crater appearance were taken to study the plasma shape, laser-induced crater appearance, and the mass of the ablated sample. The internal mechanism behind that laser-induced crater enhanced plasma radiation was researched. Under the sequential laser pulse action, the forming plasma as a result enlarges gradually first, leading to distortion at the trail of plasma plume, and then, its volume diminishes slowly. And also, the color of the plasma changes from buff to white gradually, which implies that the temperature increases constantly. The laser-induced crater had a regular shape, that is, the diameter increased from its bottom to top gradually, thus forming a taper. The mass of the laser-ablated substance descends along with increasing the amount of action pulse. Atomization degree of vaporized substance was improved in virtue of the crater confinement effect, Fresnel absorption produced from the crater walls reflection, and the inverse bremsstrahlung, and the plasma radiation intensity was enhanced as a result. PMID:19445233

Chen, Jin-Zhong; Zhang, Xiao-Ping; Guo, Qing-Lin; Su, Hong-Xin; Li, Guang

2009-02-01

349

Tuning laser-induced band gaps in graphene Hernn L. Calvo,1,2  

E-print Network

Tuning laser-induced band gaps in graphene Hernán L. Calvo,1,2 Horacio M. Pastawski,1 Stephan Roche gaps in graphene? By using Floquet theory combined with Green's functions techniques, we predict that a laser field in the mid-infrared range can produce observable band gaps in the electronic structure

350

Pump probe imaging of nanosecond laser induced bubbles in agar gel  

E-print Network

value; which should be used for eye and skin surgery. The bubble continues to grow long after the laserPump probe imaging of nanosecond laser induced bubbles in agar gel R. Evans and S. Camacho lysis: Time-resolved imaging and analysis of hydrodynamic effects," Biophysical Journal 91

Aguilar, Guillermo

351

3D Microstructure Manufacture based on laser-induced thermoplastic expansion  

Microsoft Academic Search

In this paper, we describe a novel technology for three dimensional (3D) microstructure manufacture, which is based on the laser-induced thermoplastic expansion. A thermoplastic material melted by laser heating grows in the surrounding space filled with liquid, and after the laser irradiation is switched off, it immediately solidifies into a protuberant shape because of the heat release to the liquid

Wang Leyan; Zhang Dongxian; Zhang Haijun

2006-01-01

352

Advancements in Time-Resolved X-Ray Laser Induced Time-of-Flight Photoelectron Spectroscopy.  

National Technical Information Service (NTIS)

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-...

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

2005-01-01

353

Pathogenic Escherichia coli strain discrimination using laser-induced breakdown spectroscopy  

E-print Network

Pathogenic Escherichia coli strain discrimination using laser-induced breakdown spectroscopy A pathogenic strain of bacteria, Escherichia coli O157:H7 enterohemorrhagic E. coli or EHEC , has been analyzed with both nanosecond and femtosecond laser pulses to identify the Escherichia coli bacterium.10­12 E. coli

Rehse, Steven J.

354

A new and emerging technology: Laser-induced surface modification of polymers  

Microsoft Academic Search

Laser-induced polymer surface modification is an emerging technique for imparting functional species to polymer surfaces. Laser technology, the important criteria in selecting an appropriate laser system and the principle of laser-assisted polymer surface modification are briefly discussed. Laser treatments have several benefits over other surface modification methods and new applications are being explored. Recent technological advances in laser surface modification

Murat Ozdemir; Hasan Sadikoglu

1998-01-01

355

Laser-Induced Damage Threshold and Certification Procedures for Optical Materials  

NASA Technical Reports Server (NTRS)

This document provides instructions for performing laser-induced-damage-threshold tests and pass-fail certification tests on optical materials used in pulsed-laser systems. The optical materials to which these procedures apply include coated and uncoated optical substrates, laser crystals, Q-switches, polarizers, and other optical components employed in pulsed-laser systems.

1997-01-01

356

Model of laser-induced temperature changes in solid-state optical refrigerators  

E-print Network

,10 photothermal therapy,11­13 laser-induced damage of tissue, and thermal lensing. While by the excited-state lifetime of the luminescent ion and the thermal properties of the bulk, respectively devices. © 2010 American Institute of Physics. doi:10.1063/1.3277009 I. INTRODUCTION Thermal processes

Sheik-Bahae, Mansoor

357

Use of laser-induced ionization to detect soot inception in premixed flames  

SciTech Connect

Experimental measurements of laser-induced ionization were performed for ethene-air premixed flames operated near the soot inception point. Soot was ionized with a pulsed laser operated at 532 nm. The ionization signal was collected with a tungsten electrode located in the postflame region. Ionization signals were collected by use of both single-electrode and dual-electrode configurations. Earlier laser-induced- ionization studies focused on the use of a single biased electrode to generate the electric field, with the burner head serving as the path to ground. In many practical combustion systems, a path to ground is not readily available. To apply the laser-induced- ionization diagnostic to these geometries, a dual-electrode geometry must be employed. The influence of electrode configuration, flame equivalence ratio, and flame height on ionization signal detection was determined. The efficacy of the laser-induced-ionization diagnostic in detecting soot inception in the postflame region of a premixed flame by use of a dual-electrode configuration was investigated. Of the dual-electrode configurations tested, the dual-electrode geometry oriented parallel to the laser beam was observed to be most sensitive for detecting the soot inception point in a premixed flame.

Manzello, Samuel L.; Lee, Eui Ju; Mulholland, George W

2005-08-20

358

Laser-induced fluorescence measurements in an inductively coupled plasma reactor  

E-print Network

Laser-induced fluorescence measurements in an inductively coupled plasma reactor Brett Jacobs velocity distribution functions made in an inductively coupled plasma reactor with a pulsed plasma source coupled plasma source 400 Hz repetition rate at 400 kHz . The in- stantaneous plasma source power was 4 k

California at Los Angles, University of

359

Particle image velocimetry and planar laser-induced fluorescence measurements on lobed jet mixing flows  

E-print Network

Particle image velocimetry and planar laser-induced fluorescence measurements on lobed jet mixing-induced ¯uores- cence (PLIF) and particle image velocimetry (PIV) were used to accomplish ¯ow visualisation character- istics downstream of a lobed nozzle/mixer systematically by using laser Doppler velocimetry (LDV

Hu, Hui

360

Particle streak velocimetry and CH laser-induced fluorescence diagnostics in strained, premixed,  

E-print Network

Particle streak velocimetry and CH laser-induced fluorescence diagnostics in strained, premixed, 91125 Abstract We present the use of simultaneous Particle Streak Velocimetry (PSV) and CH Planar Laser Streak Velocimetry (PSV) [1­3], a tech- nique similar to particle tracking velocimetry [4], is used

Barr, Al

361

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

362

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

E-print Network

EFFECT OF LASER INDUCED CRYSTALLINITY MODIFICATION ON BIODEGRADATION PROFILE OF POLY(L-LACTIC ACID attention due to their biocompatibility and biodegradability. Being biodegradable, poly(L-lactic acid) (PLLA it favorable in drug delivery because it hydrolyzes in the human body into lactic acid, which is then excreted

Yao, Y. Lawrence

363

Ex vivo optical coherence tomography and laser induced fluorescence spectroscopy imaging of murine gastrointestinal tract  

Microsoft Academic Search

Optical Coherence Tomography (OCT) and Laser Induced Fluorescence Spectroscopy (LIF) have separately been found to have clinical potential in identifying human gastrointestinal (GI) pathologies, yet their diagnostic capability in mouse models of human disease is unknown. We combine the two modalities to survey the GI tract of a variety of mouse strains and sample dysplasias and inflammatory bowel disease (IBD)

Lida Hariri; Norman Wade; David Besselsen; Urs Utzinger; Eugene Gerner; Jennifer Barton

2005-01-01

364

Monitoring glucose in vivo by measuring laser-induced acoustic profiles  

Microsoft Academic Search

The optoacoustic method of monitoring absorbed optical energy distribution in tissues was employed to measure changes in glucose concentration in vivo. Glucose osmotic and hydrophilic properties cause reduction of tissue scattering as a result of glucose concentration increase around scattering particles and fibers. The opto-acoustic (OA) method utilizes time-resolved measurements of laser- induced ultrasonic profile in tissue resembling the distribution

Andrey A. Bednov; Alexander A. Karabutov; Elena V. Savateeva; Wayne F. March; Alexander A. Oraevsky

2000-01-01

365

Laser-induced thermotherapy of benign and malignant tumors controlled by color-coded duplex sonography  

Microsoft Academic Search

Since 1984 we use the interstitial application of laser induced thermotherapy (LITT) for the treatment of congenital vascular disorders (CVD) such as hemangiomas and vascular malformations. In most of the procedures a 600 micron core bare fiber is used to deliver the radiation of a cw Nd:YAG laser emitting at 1064 nm into the diseased tissue. As most of the

Carsten M. Philipp; Ewa Rohde; Juergen Waldschmidt; Hans-Peter Berlien

1994-01-01

366

Plasma volume considerations for analysis of gaseous and aerosol samples using laser-induced breakdown spectroscopy  

E-print Network

of laser- induced plasma-particle interactions. Due to plasma non-homogeneity, the particle vaporizationPlasma volume considerations for analysis of gaseous and aerosol samples using laser and diffusion, and is considered in terms of an equivalent emitting plasma volume. Introduction Laser

Hahn, David W.

367

Laser-induced breakdown spectrometry — applications for production control and quality assurance in the steel industry  

Microsoft Academic Search

Recent progress in sensitivity and signal processing opened a broad field of application for laser-induced breakdown spectrometry (LIBS) in the steel making and processing industry. Analyzed substances range from top gas of the blast furnace, via liquid steel up to finished products. This paper gives an overview of R&D activities and first routine industrial applications of LIBS. The continuous knowledge

Reinhard Noll; Holger Bette; Adriane Brysch; Marc Kraushaar; Ingo Mönch; Laszlo Peter; Volker Sturm

2001-01-01

368

Laser-induced breakdown spectroscopy (LIBS): An innovative tool for studying bacteria  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) has gained a reputation as a flexible and convenient technique for rapidly determining the elemental composition of samples with minimal or no sample preparation. In this dissertation, I will describe the benefits of using LIBS for the rapid discrimination and identification of bacteria (both pathogenic and non-pathogenic) based on the relative concentration of trace inorganic elements

Qassem I Mohaidat

2011-01-01

369

Laser-induced breakdown spectroscopy (libs): an innovative tool for studying bacteria  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) has gained a reputation as a flexible and convenient technique for rapidly determining the elemental composition of samples with minimal or no sample preparation. In this dissertation, I will describe the benefits of using LIBS for the rapid discrimination and identification of bacteria (both pathogenic and non-pathogenic) based on the relative concentration of trace inorganic elements

Qassem I. Mohaidat

2011-01-01

370

Fabrication of LCD color filter using laser-induced thermal spray printing  

Microsoft Academic Search

The color filter of the LCD panel is fabricated using the laser induced thermal spray printing (LITSP) method, which ejects the ink droplets from the blind-holes of the donor plate to the substrate by the bubble pressure due to rapid laser heating. The compositions of the dye and pigment inks are determined experimentally, which consists of 5% colorant, 24% epoxy,

Jae Hak Lee; Seong Joon Na; Choong Don Yoo; Yong-Seog Kim

2008-01-01

371

Non-intrusive temperature measurements using three-color laser-induced fluorescence  

Microsoft Academic Search

This paper presents a new temperature measurement technique in a liquid, based on laser-induced fluorescence of rhodamine B. The fluorescence intensity is detected on three spectral bands, where the ratios between the emission of each band determine the temperature while correcting for the effects of fluorescent re-absorption. In addition, the influence of parameters such as probe volume size, dye concentration,

P. Lavieille; A. Delconte; D. Blondel; M. Lebouché; F. Lemoine

2004-01-01

372

Spectroscopic temperature measurements in a decaying laser-induced plasma using the C2 Swan system  

Microsoft Academic Search

Spontaneous emission spectra of C2 Swan bands were recorded well after i.r. 1064 nm Nd: YAG laser-induced optical breakdown of carbon monoxide. Temperatures in excess of 6000 K were determined using fits to synthetic diatomic molecular spectra.

Christian Parigger; David H. Plemmons; James O. Hornkohl; J. W. Lewis

1994-01-01

373

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

374

Analysis of laser induced acoustic pulse probing of charge distributions in dielectrics  

E-print Network

energy conversion effi- ciency. 3) The influence of the elastic properties of the materialL-171 Analysis of laser induced acoustic pulse probing of charge distributions in dielectrics C'impulsions de pression sans variation notable de la forme de ces impulsions, avec un bon rendement de conversion

Boyer, Edmond

375

Thermal excitation of d band electrons in Au: implications for laser-induced phase transformations  

E-print Network

Thermal excitation of d band electrons in Au: implications for laser-induced phase transformations of the electron heat capacity and the electron-phonon coupling factor are investigated for Au based on the electron density of states obtained from ab initio electronic structure calculations. Thermal excitation

Zhigilei, Leonid V.

376

Carbon dioxide UV laser-induced fluorescence in high-pressure flames  

E-print Network

Carbon dioxide UV laser-induced fluorescence in high-pressure flames W.G. Bessler a , C. Schulz a dioxide is investigated with excitation between 215 and 255 nm with spectrally resolved detection in 5 dioxide (CO2) and water (H2O), based on mea- surements in engines [11] and high-pressure flames [12

Lee, Tonghun

377

Transient Fluorescence Spectroscopy and laser induced fluorescence lifetimes of terbium doped dipicolinic acid  

NASA Astrophysics Data System (ADS)

We have investigated the use of deep UV laser induced fluorescence for the sensitive detection and spectroscopic lifetime studies of terbium doped dipicolinic acid (DPA-Tb) and used this to study the optical characteristics of DPA which is a chemical surrounding most bacterial spores. Background absorption spectra, fluorescence spectra, and Excitation Emission Matrix (EEM) spectra were made of the DPA-Tb complex, using both fixed 266 nm wavelength and tunable (220 nm--280 nm) UV laser excitations. Of importance, the fluorescence lifetimes of the four main fluorescence peaks (488 nm, 543 nm, 581 nm, and 618 nm) of the DPA-Tb complex have been measured for the first time to our knowledge. The lifetimes of all the fluorescing lines have been measured as a function of DPA-Tb concentration, solvent pH, and solvent composition, including that for the weakest fluorescing line of DPA-Tb at 618 nm. In addition, a new spectroscopic lifetime measurement technique, which we call "Transient Fluorescence Spectroscopy", was developed. In this technique, a weak, quasi-CW, amplitude modulated UV laser (8.5 kHz) was used to measure the lifetimes of the fluorescence lines, and yields insight into energy transfer and excitation lifetimes within the system. This technique is especially useful when a high power laser is not either available or not suitable. In the latter case, this would be when a high power pulsed deep-UV laser could produce bleaching or destruction of the biological specimen. In addition, this technique simulated the excitation and fluorescence emission of the DPA-Tb using a 4-level energy model, and solved the dynamic transient rate equations to predict the temporal behavior of the DPA-Tb emitted fluorescence. Excellent agreement between the experiments and the simulation were found. This technique has the potential to provide a more accurate value for the fluorescence lifetime values. In addition, with the use of asymmetric excitation waveforms, the dynamic transient rate equation analysis may allow for detailed studies of selected transfer mechanisms in a wide range of other spectroscopic applications including rare-earth solid-state lasing materials and biological samples.

Makoui, Anali

378

Transcutaneous laser-induced interstitial thermotherapy of nodular goiter  

Microsoft Academic Search

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

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

2000-01-01

379

Transcutaneous laser-induced interstitial thermotherapy of nodular goiter  

Microsoft Academic Search

In the experiment on 41 dogs the possibilities of Nd:YAG (1064nm) and diode lasers (805nm) 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

Valery A. Privalov; Oleg V. Seliverstov; Jean A. Revel-Muroza; Alexander V. Lapp; Ravil U. Giniatullina

380

Chirped diffraction grating optical switching  

NASA Astrophysics Data System (ADS)

While fiber optic Bragg grating sensors have emerged as a viable commercial product and principle component within numerous fiber optic components, they possess the inherent inflexibility that once written, the nonstressed grating spacing is fixed. An alternative method of fabricating Bragg gratings where a photosensitive fiber core material (similar to that used in photogrey sunglasses) exists at the grating site along the fiber has been examined. As opposed to a conventional grating writing method using lateral illumination of the fiber core, in this instance the diffraction rating is written via a deliberate intensity variation in the light which is injected into the fiber. The slight difference in refractive index between the photogrey section of the core and the regular fiber causes an internal Fabry-Perot resonator cavity to be established. By using an intensity-modulated high power laser, the illuminating modulation pattern reflects back and forth within this cavity establishing a standing wave pattern. Different patterns may be launched into the fiber resulting in a grating spacing which is variable. This standing wave pattern effectively illuminates the photogrey section nonuniformly with the high power portions of the standing wave pattern causing more darkening - thereby in essence creating the Bragg diffraction grating. Removal of this illumination source results in a grating that fades away yielding a re-writable component. An examination of this type or re-writable component will be reported along with its suitability for 100- and 5-GHz DWDM applications.

Fuhr, Peter L.; Spremo, Stevan

2002-05-01

381

Toroidal Varied-Line Space (TVLS) Gratings  

NASA Technical Reports Server (NTRS)

It is a particular challenge to develop a stigmatic spectrograph for XUV wavelengths since the very low normal-incidence reflectance of standard materials most often requires that the design be restricted to a single optical element which must simultaneously provide both re-imaging and spectral dispersion. This problem has been solved in the past by the use of toroidal gratings with uniform line-spaced rulings (TULS). A number of solar EUV (Extreme Ultraviolet) spectrometers have been based on such designs, including SOHO/CDS, Solar-B/EIS, and the sounding rockets SERTS and EUNIS. More recently, Kita, Harada, and collaborators have developed the theory of spherical gratings with varied line-space rulings (SVLS) operated at unity magnification, which have been flown on several astronomical satellite missions. We now combine these ideas into a spectrometer concept that puts varied-line space rulings onto toroidal gratings. Such TVLS designs are found to provide excellent imaging even at very large spectrograph magnifications and beam-speeds, permitting extremely high-quality performance in remarkably compact instrument packages. Optical characteristics of two solar spectrometers based on this concept are described: SUMI, proposed as a sounding rocket experiment, and NEXUS, proposed for the Solar Dynamics Observatory mission.

Thomas, Roger J.; Oegerle, William (Technical Monitor)

2002-01-01

382

Ignition characteristics of methane/air premixed mixture by microwave-enhanced laser-induced breakdown plasma.  

PubMed

A microwave-enhanced plasma generation technique was combined with laser-induced ignition to improve ignition characteristics. A locally intensified microwave field was formed near the laser-induced breakdown plasma. As the plasma absorbed the microwaves, the plasma emission intensity increased. The plasma lifetime could be controlled by changing the microwave oscillation duration. Furthermore, the microwave-enhanced laser-induced breakdown plasma improved the minimum ignition energy of the methane/air pre-mixture with just a small amount of absorbed microwave energy. PMID:24514928

Nishiyama, Atsushi; Moon, Ahsa; Ikeda, Yuji; Hayashi, Jun; Akamatsu, Fumiteru

2013-11-01

383

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

384

Imaging laser-induced thermal fields and effects  

NASA Astrophysics Data System (ADS)

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

Verdaasdonck, Rudolf M.

1995-05-01

385

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

386

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

387

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

388

Research of fiber Bragg grating geophone based on cantilever beam  

NASA Astrophysics Data System (ADS)

Along with the development of seismic exploration, the demand of frequency, dynamic range, precision and resolution ration is increased. However, the traditional geophone has disadvantages of narrower bandwidth, lower dynamic range and resolution, and cannot meet the new needs of seismic exploration. Geophone technology is a choke point, which constrains the development of petroleum prospecting in recent years. Fiber Bragg Grating seism demodulation technology is the newest kind of seism demodulation technology. The sensing probe of the Fiber Bragg Grating geophone is made up of Fiber Bragg Gating. The information which it collects is embodied by wavelength. The modulation-demodulation is accomplished by Fiber Bragg Gating geophone directly. In this paper, we design different size Fiber Bragg Grating geophones based on the transmission properties of Fiber Bragg Grating and cantilever beam method. Beryllium bronze and stainless steel are chosen as the elastic beam and shell materials, respectively. The parameters such as response function and sensitivity are given theoretically. In addition, we have simulated the transmission characteristics of Fiber Bragg Grating geophone by virtue of finite element analysis. The influences of wavelength, mass block, fiber length on the characteristics of geophones are discussed in detail, and finally the appropriate structural parameters are presented.

Wang, Liang; Chen, Shao-hua; Tao, Guo; Lu, Gui-wu; Zhao, Kun

2009-07-01

389

Self-heated fiber Bragg grating sensors  

Microsoft Academic Search

This letter demonstrates an approach for tuning fiber Bragg grating sensors with optical energy carried in the same optical fiber. Optical energy carried in the optical fiber was used to heat in-fiber Bragg gratings in order to alter the grating's optical response to surrounding media. The functional enhancement of optically heated Bragg gratings as sensor devices is demonstrated by a

Kevin P. Chen; Ben McMillen; Michael Buric; Chuck Jewart; Wei Xu

2005-01-01

390

Thermal and Structural Analysis of FIMS Grating  

Microsoft Academic Search

Far ultraviolet IMaging Spectrograph (FIMS) should be designed to maintain its structural stability and to minimize optical performance degradation in launch and in operation enviroments. The structural and thermal analyzes of grating and grating mount system, which are directly related to FIMS optical performance, was performed using finite element method. The grating mount was made to keep the grating stress

K.-I. Seon; I.-S. Yuk; K.-S. Ryu; J.-H. Park; K. Kang; H. Jin; U.-W. Nam; W. Han; K.-W. Min; W.-B. Lee; J. Edelstein; E. Korpela

2001-01-01

391

Implications of transient changes of optical and surface properties of solids during femtosecond laser pulse irradiation to the formation of laser-induced periodic surface structures  

NASA Astrophysics Data System (ADS)

The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of silicon wafer surfaces by linearly polarized Ti:sapphire femtosecond laser pulses (pulse duration 130 fs, central wavelength 800 nm) is studied experimentally and theoretically. In the experiments, so-called low-spatial frequency LIPSS (LSFL) were found with periods smaller than the laser wavelength and an orientation perpendicular to the polarization. The experimental results are analyzed by means of a new theoretical approach, which combines the widely accepted LIPSS theory of Sipe et al. with a Drude model, in order to account for transient (intra-pulse) changes of the optical properties of the irradiated materials. It is found that the LSFL formation is caused by the excitation of surface plasmon polaritons, SPPs, once the initially semiconducting material turns to a metallic state upon formation of a dense free-electron-plasma in the material and the subsequent interference between its electrical field with that of the incident laser beam resulting in a spatially modulated energy deposition at the surface. Moreover, the influence of the laser-excited carrier density and the role of the feedback upon the multi-pulse irradiation and its relation to the excitation of SPP in a grating-like surface structure is discussed.

Bonse, J.; Rosenfeld, A.; Krüger, J.

2011-04-01

392

Measurement and analysis of atomic hydrogen and diatomic molecular AlO, C2, CN, and TiO spectra following laser-induced optical breakdown.  

PubMed

In this work, we present time-resolved measurements of atomic and diatomic spectra following laser-induced optical breakdown. A typical LIBS arrangement is used. Here we operate a Nd:YAG laser at a frequency of 10 Hz at the fundamental wavelength of 1,064 nm. The 14 nsec pulses with anenergy of 190 mJ/pulse are focused to a 50 µm spot size to generate a plasma from optical breakdown or laser ablation in air. The microplasma is imaged onto the entrance slit of a 0.6 m spectrometer, and spectra are recorded using an 1,800 grooves/mm grating an intensified linear diode array and optical multichannel analyzer (OMA) or an ICCD. Of interest are Stark-broadened atomic lines of the hydrogen Balmer series to infer electron density. We also elaborate on temperature measurements from diatomic emission spectra of aluminum monoxide (AlO), carbon (C2), cyanogen (CN), and titanium monoxide (TiO). The experimental procedures include wavelength and sensitivity calibrations. Analysis of the recorded molecular spectra is accomplished by the fitting of data with tabulated line strengths. Furthermore, Monte-Carlo type simulations are performed to estimate the error margins. Time-resolved measurements are essential for the transient plasma commonly encountered in LIBS. PMID:24561875

Parigger, Christian G; Woods, Alexander C; Witte, Michael J; Swafford, Lauren D; Surmick, David M

2014-01-01

393

Laser induced electron acceleration in an ion-channel guiding  

SciTech Connect

Direct electron acceleration by a propagating laser pulse of circular polarization in an ion-channel guiding is studied by developing a relativistic three-dimensional single particle code. The electron chaotic dynamic is also studied using time series, power spectrum, and Liapunov exponent. It is found that the electron motion is regular (non-chaotic) for laser pulse with short time duration, while for long enough time duration, the electron motion may be chaotic. In the case of non-chaotic motion, the electron can gain and retain very high energy in the presence of ion-channel before reaching the steady-state, whereas in the case of chaotic motion, the electron gains energy and then loses it very rapidly in an unpredictable manner.

Esmaeilzadeh, Mahdi; Taghavi, Amin; Hanifpour, Maryam [Department of physics, Iran University of Science and Technology, Narmak, Tehran 16844 (Iran, Islamic Republic of)

2011-09-15

394

Process analysis of recycled thermoplasts from consumer electronics by laser-induced plasma spectroscopy.  

PubMed

An experimental setup for direct elemental analysis of recycled thermoplasts from consumer electronics by laser-induced plasma spectroscopy (LIPS, or laser-induced breakdown spectroscopy, LIBS) was realized. The combination of a echelle spectrograph, featuring a high resolution with a broad spectral coverage, with multivariate methods, such as PLS, PCR, and variable subset selection via a genetic algorithm, resulted in considerable improvements in selectivity and sensitivity for this complex matrix. With a normalization to carbon as internal standard, the limits of detection were in the ppm range. A preliminary pattern recognition study points to the possibility of polymer recognition via the line-rich echelle spectra. Several experiments at an extruder within a recycling plant demonstrated successfully the capability of LIPS for different kinds of routine on-line process analysis. PMID:12236340

Fink, Herbert; Panne, Ulrich; Niessner, Reinhard

2002-09-01

395

Multiple pulse nanosecond laser induced damage study in LiB3O5 crystals.  

PubMed

Multiple pulse nanosecond laser induced damage in the bulk of LiB3O5 (LBO) crystals was investigated at 1064 nm, 532 nm and 355 nm. Scanning electron microscopy of cleaved damage sites confirmed the presence of different zones that have already been reported in the case of KH2PO4 (KDP). Multi pulse measurements reveal a strong decrease of the damage threshold with increasing pulse number at 1064 nm (fatigue effect). A weaker fatigue effect was observed at 532 nm and no fatigue effect was found at 355 nm. This observation is best explained by an inherently statistical light matter interaction generating laser induced damage. Finally, a polarization dependent damage threshold anisotropy was evidenced at all three wavelengths, being strongest at 1064 nm. The results indicate the importance of Li+ vacancy stabilized color centers for the damage mechanism. PMID:21196955

Wagner, Frank R; Hildenbrand, Anne; Natoli, Jean-Yves; Commandré, Mireille

2010-12-20

396

Laser-induced damage of multilayer high-reflectance coatings for 248 nm  

NASA Astrophysics Data System (ADS)

In order to study the effect of material properties on the laser induced damage of dielectric coatings at a wavelength of 248 nm, multilayer coatings were deposited by electron beam reactive evaporation technique onto fused silica substrates with the materials of hafnium oxide, aluminum oxide and silicon dioxide. Laser-induced damage thresholds (LIDTs), morphologies and profiles of damage sites of multilayer thin films were measured to investigate the damage mechanism. Besides, with our programmed software, the temperature rise in the multilayers was calculated to better understand the relationship between damage morphology, electric field peak location and depth of damage sites. The results indicate that the absorption of defect and the electric field distribution of thin film greatly contribute to LIDTs of thin films, and the control of defect, especially defect with strong absorption, is still the only way to improve the laser radiation resistivity of coatings in the UV spectral region.

Qi, Hongji; Yi, Kui; Yu, Hua; Cui, Yun; Li, Dawei; Gao, Zhixing; Shao, Jianda; Fan, Zhengxiu

2008-01-01

397

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

398

Fast laser-induced aerosol formation for visualization of gas flows  

NASA Technical Reports Server (NTRS)

A technique for aerosol seeding of gas flows by laser-induced particle formation is demonstrated using a pulsed Nd:YAG laser (1.06 microns) for optical breakdown of a mixture of SF6 and H2 in an inert carrier gas. It is noted that, contrary to the smoke-wire approach, the laser-induced particles form first in zones of high turbulence, since mixing enhances coagulation. The method also allows seeding to be performed in locations hardly accessible otherwise and is mechanically nonintrusive. Finally, a study of the mixture and the breakdown effects indicates that for H2:SF6 ratios between 3:1 and 15:1 the particle formation is only limited by the physics of the gas/particle conversion.

Hassa, C.; Hanson, R. K.

1985-01-01

399

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

400

Nanosecond laser-induced periodic surface structuring of cross-linked azo-polymer films  

NASA Astrophysics Data System (ADS)

In this work we discuss the response to laser ablation of a poly(4-vinylbenzyl azide-random-methyl methacrylate) (p((S-N3)-r-MMA)) random copolymer. This material is cross-linkable thermally and upon exposure to UV light, and on cross-linked films the irradiation with a 248 nm ns KrF laser induces the formation of laser induced periodical surface structure (LIPSS). The LIPSS morphology is dependent on the amount of 4-vinylbenzyl azide (S-N3) groups in the pristine copolymer. We propose a crosslinking mechanism based on the scission of azide with formation of azo groups and we discuss the possible relationship between this chemical modifications and the formation of ripples on the bottom of laser ablation cavities.

Berta, Marco; Biver, Émeric; Maria, Sébastien; Phan, Trang N. T.; D'Aleo, Anthony; Delaporte, Philippe; Fages, Frederic; Gigmes, Didier

2013-10-01

401

Laser-induced radical generation and evolution to a self-sustaining flame  

SciTech Connect

Images and emission spectra of sparks produced by laser-induced breakdown of methane and propane air mixtures were investigated with a high degree of spatial and temporal resolution. The laser-induced breakdown was generated by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser. The data were collected using an intensified high-speed camera and a single/multi-fiber Cassegrain optics system coupled to an ICCD spectrometer. Emission spectra of OH{sup *}, CN{sup *}, CH{sup *}, and C{sup *}{sub 2} radicals were also collected using spectra boxes. The results provided information about the different stages of the laser-induced breakdown, with a specific focus on the transition from a flame kernel to a self-sustaining flame. The plasma shape and emission spectrum were very reproducible. The differences in the size of the flame kernel and the evolution of the radical emissions were analyzed for mixtures that fired or misfired. The impact of the level of radicals in the flame kernel was a critical parameter for the firing process, starting around 1 {mu}s after the laser-induced breakdown. The transition from plasma cooling to the classical chemical reactions in the combustion zone was analyzed. Even though the flame kernel size was directly linked to the spark energy, this was not a key parameter toward evolution to a self-sustaining flame. The Taylor blast wave theory was used to plot the location of the shock based on the evolution of the flame kernel size. The location was calculated using a laser-supported detonation model. A very good correlation was observed with the hot gas ignition process. Our results allowed us to obtain information about the process leading to firing or misfiring for similar environments, resulting in a better understanding of the laser breakdown phenomena and the means of utilizing this technique in an industrial context. (author)

Beduneau, J.L. [CORIA UMR 6614 CNRS, INSA Avenue de l'Universite BP8, 76801 Saint Etienne du Rouvray Cedex (France); Kawahara, N.; Nakayama, T.; Tomita, E. [Department of Mechanical Engineering, Okayama University, Tsushima-Naka 3, Okayama 700-8530 (Japan); Ikeda, Y. [Imagineering, Inc., Welv Rokko 2nd Bldg. 3F, 4-1-1 Fukada, Nada, Kobe 657-0038 (Japan)

2009-03-15

402

Laser-induced fluorescence measurements of three plasma species with a tunable diode laser  

SciTech Connect

Recently, we demonstrated that a single, tunable, low-power, diode laser can be used for laser-induced fluorescence (LIF) measurements of both argon ions and helium neutrals. We have now identified a third fluorescence scheme, for neutral argon atoms, accessible with the same tunable diode laser. Fluorescence measurements of a heated iodine cell are used to monitor the wavelength of the laser during the LIF measurement.

Keesee, Amy M.; Scime, Earl E.; Boivin, Robert F. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506-6315 (United States); Department of Physics, Auburn University, Aubum, Alabama 36849-5311 (United States)

2004-10-01

403

Planar laser-induced fluorescence measurements of high-enthalpy free jet flow with nitric oxide  

NASA Technical Reports Server (NTRS)

Planar laser-induced fluorescence (PLIF) measurements of property fields in a high-enthalpy, supersonic, underexpanded free jet generated in a reflection-type shock tunnel are reported. PLIF images showing velocity and temperature sensitivity are presented. The inferred radial velocity and relative rotational temperature fields are found to be in agreement with those predicted by a numerical simulation of the flowfield using the method of characteristics.

Palmer, Jennifer L.; Mcmillin, Brian K.; Hanson, Ronald K.

1992-01-01

404

Optical fiber measurements of particle velocity using laser-induced phosphorescence  

SciTech Connect

An optical fiber anemometer that uses laser-induced phosphorescence to measure particle time of flight in dense gas-solid suspensions is described. The anemometer is tested using a spinning disk coated with a phosphor having a persistent afterglow. The diagnostic technique is illustrated by measuring the velocity of free-falling particles coated with the same phosphor. Monte Carlo simulations are employed to determine the optical characteristics of the probe, including its measurement volume.

Louge, M.Y. (Cornell University, Ithaca, New York 14853-7501 (USA)); Iyer, S.A.; Giannelis, E.P. (Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853-7501 (USA)); Lischer, D.J.; Chang, H. (Sibley School of Mechanical Aerospace Engineering, Cornell University, Ithaca, New York 14853-7501 (USA))

1991-05-20

405

Spatially resolved measurement of femtosecond laser induced refractive index changes in transparent materials.  

PubMed

We present a practical method to determine femtosecond laser induced refractive index changes in transparent materials. Based on an iterative Fourier transform algorithm, this technique spatially resolves the refractive index of complex structures by combining the dimensions of the modified region with the corresponding phase change extracted from far-field intensity measurements. This approach is used to characterize optical waveguides written by a femtosecond laser in borosilicate glass. PMID:22825206

Berlich, René; Choi, Jiyeon; Mazuir, Clarisse; Schoenfeld, Winston V; Nolte, Stefan; Richardson, Martin

2012-07-15

406

Onset of Material Alterations Due to Laser-Induced Plasma Exposure in Nanofilms Deposited on Photomasks  

Microsoft Academic Search

Damage-free removal of sub-100 nm particles from photomasks with deposited nanofilms is a challenge in lithography. Laser-induced plasma (LIP) is an emerging noncontact, chemical-free, dry, and selective nanoparticle removal technique. Investigation of the onset of material alterations on bonded nanofilms for optimizing LIP particle removal process is the objective of this paper. Shockwave thermomechanical excitation and radiation heating from the

Ivin Varghese; Dong Zhou; M. D. Murthy Peri; Cetin Cetinkaya

2009-01-01

407

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

408

A time-gating scintillation detector for the measurement of laser-induced fast neutrons  

SciTech Connect

A time-gating scintillation detector, in which a fast high voltage switch is used for gating a channel photomultiplier, was developed for a measurement of laser-induced fast neutrons. The x rays generated from the intense femtosecond laser and the solid target interactions were suppressed selectively and a time-of-flight signal of a laser-generated fast neutron was measured effectively. The detector was used successfully to measure the neutron yield of a femtosecond, deuterated, polystyrene plasma.

Lee, Sungman; Park, Sangsoon; Yea, Kwon-hae; Cha, Hyungki [Quantum Optics Division, Korea Atomic Energy Research Institute, Daejeon 305-600 (Korea, Republic of)

2009-06-15

409

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

410

Combined Raman spectrometer\\/laser-induced breakdown spectrometer for the next ESA mission to Mars  

Microsoft Academic Search

Among the different instruments that have been pre-selected to be on-board the Pasteur payload on ExoMars is the Raman\\/laser induced breakdown spectroscopy (LIBS) instrument. Raman spectroscopy and LIBS will be integrated into a single instrument sharing many hardware commonalities.An international team under the lead of TNO has been gathered to produce a design concept for a combined Raman spectrometer\\/LIBS elegant

Grégory Bazalgette Courrèges-Lacoste; Berit Ahlers; Fernando Rull Pérez

2007-01-01

411

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

412

Highly Time Resolved Measurements of OH during POPCORN Using Laser-Induced Fluorescence Spectroscopy  

Microsoft Academic Search

Tropospheric hydroxyl radical (OH) concentrations were measured by laser-induced fluorescence (LIF) during the POPCORN field campaign in August 1994 at a rural site in the North East of Germany. Ambient air spectra were recorded by tuning the laser wavelength over a spectral region covering the Q11(3), Q21(3), and P11(1) rotational transitions of the (0-0) band in the A-X system of

F. Holland; U. Aschmutat; M. Heßling; A. Hofzumahaus; D. H. Ehhalt

1998-01-01

413

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

414

Acoustic detection of controlled laser-induced microbubble creation in gelatin  

Microsoft Academic Search

A high-frequency (85 MHz) acoustic technique is used to identify system parameters for controlled laser-induced microbubble creation inside tissue-mimicking, gelatin phantoms. Microbubbles are generated at the focus of an ultrafast 793-nm laser source and simultaneously monitored through ultrasonic pulse-echo recordings. Displayed in wavefield form, these recordings illustrate microbubble creation, and integrated backscatter plots provide specifics about microbubble characteristics arid dissolution

Christine Tse; Marwa J. Zohdy; Jing Yong Ye; Theodore B. Norris; Lajos P. Balogh; Kyle W. Hollman; M. O'Donnell

2005-01-01

415

Study of laser induced stress waves emerged by laser-target interaction  

NASA Astrophysics Data System (ADS)

Laser induced emergent stress wave (LIESW) generated by interaction between laser and target. LIESW can be emerged by the following complicated mechanisms: Optical breakdown, ablation and plasma formations, and stress wave with recoil momentum. We propose a method of gene transfection using LIESW. This method has several advantages such as a nonchemical, nonviral, and noninvasive and so on. In this report, we report a summary of our research.

Nishiwaki, Motoaki; Kogi, Mieko; Aizawa, Koji; Tokunaga, Yoshiaki

2012-09-01

416

Detection of Aerosol Particles by Time-Resolved Laser Induced Breakdown Spectroscopy and its Emission Properties  

NASA Astrophysics Data System (ADS)

Development of in-situ and real-time detection techniques for is strongly expected for the human health and public welfare. Particles of SPM size in the air can be exploded by a focused high power laser pulse, and the concentration and composition of the particles are observed by measuring the intensity and the spectra of plasma emission of the particles exploded. Laser induced breakdown spectroscopy is a conventional detection method based on this particle explosion. In the present work, the time-resolved technique was combined with the laser induced breakdown spectroscopic method, in order to improve the signal/noise ratio and efficiency. In this work, firstly, the time-resolved laser induced breakdown spectroscopy system was established in the laboratory and the CaCO3 particles flowing in the air was detected by measuring the Ca II emission at 396nm. Linear calibration curve was obtained between 1x10-4g/m3-5x10-4g/m3 for CaCO3 particles. Secondly, we studied whether TiO2 particles in the presence and in the absence of Eu on their surface could be distinguished by the time-resolved laser induced breakdown spectroscopy. It was found that the dependence of peak intensity of Ti I emission at 453 nm on the laser power consisted of two regions for low Eu loading and of one for high Eu loading. This difference is considered to be caused by different mechanisms in initial electron density formation, suggesting that TiO2 particles in the presence and in the absence of Eu on their surface was distinguished.

Nagasaki, S.; Tanaka, Y.; Kado, S.; Tanaka, S.

2001-12-01

417

Color-coded duplex sonography as a new method for monitoring of laser-induced thermotherapy  

NASA Astrophysics Data System (ADS)

The aim of our experimental and clinical studies was to investigate the suitability of Color- Coded Duplex Sonography (CCDS) for on-line monitoring of the Laser-Induced Thermotherapy procedures. Both the changes in the CCDS imaging during irradiation as well as the thresholds at which a `color bruit' occurs were investigated. Furthermore we have evaluated the correlation between the B-scan imaging of the damaged area and the size of coagulation in pathology measurements.

Philipp, Carsten M.; Bollow, Matthias; Krasicka-Rohde, Ewa; Fobbe, Franz; Berlien, Hans-Peter

1994-05-01

418

Two-wavelength interferometry on excimer laser induced vapour\\/plasma plumes during the laser pulse  

Microsoft Academic Search

Ablation-using short-pulse lasers, e.g., excimer lasers and solid state lasers, is becoming an important technology for micro-machining, thin film formation and fine particle generation. Hence, there is a great interest to understand the interaction mechanisms between the radiation field and the evaporated material. Especially the laser-induced material vapour influences the efficiency and the quality of the ablation, as shown in

H. Schittenhelm; G. Callies; P. Berger; H. Hügel

1998-01-01

419

Tunable ultraviolet laser-induced fluorescence detection of trace plastics and dissolved organic compounds in water  

Microsoft Academic Search

We developed a tunable (220-285-nm) UV and fixed 266-nm laser-induced fluorescence (LIF) system using a spectrometer and a cooled CCD imaging detector to measure the excitation-emission matrix spectra of various compounds in water, including quinine sulfate and plastic compound bisphenol-A. The LIF instrument was used for the fast, nonspecific determination of trace amounts of dissolved organic compounds present in natural

Vasanthi Sivaprakasam; Dennis K. Killinger

2003-01-01

420

Pulsed laser-induced electrical-current joule heating for crystallization of silicon thin films  

Microsoft Academic Search

50 nm-amorphous silicon films were crystallized by the pulsed laser-induced electrical-current joule heating method. Holes with diameter of 6 mum were formed within silicon strips, in order to control the position of the formation of crystalline grains. Large crystalline grains of 10 mum were formed between the holes in lateral direction from the observation of the photograph of the optical

Nobuyuki Andoh; Toshiyuki Sameshima

2004-01-01

421

Pulsed-laser-induced dewetting in nanoscopic metal films: Theory and experiments  

Microsoft Academic Search

Hydrodynamic pattern formation (PF) and dewetting resulting from pulsed-laser-induced melting of nanoscopic metal films have been used to create spatially ordered metal nanoparticle arrays with monomodal size distribution on SiO2\\/Si substrates. PF was investigated for film thickness h<=7nmEm , where Em denotes the h -dependent threshold energy required to melt the film. Even at such small length scales, theoretical predictions

Justin Trice; Dennis Thomas; Christopher Favazza; Radhakrishna Sureshkumar; Ramki Kalyanaraman

2007-01-01

422

Laser-Induced Damage Threshold and Surface Processing of GaN at 400 nm Wavelength  

Microsoft Academic Search

The laser-induced damage of epitaxially grown GaN semiconductor material is investigated for the first time by illumination of the c-plane by sub-picosecond laser pulses at the wavelength of 400 nm. The surface damage was investigated by optical and atomic force microscopies. The threshold fluence for ablation damage is determined to be ˜5.4 J\\/cm2 for pulse width of 150 fs. An

Petr G. Eliseev; Hong-Bo Sun; Saulius Juodkazis; Tomoya Sugahara; Shiro Sakai; Hiroaki Misawa

1999-01-01

423

SEPARATION OF HISTORICAL DYES USING CAPILLARY ELECTROPHORESIS WITH LASER-INDUCED FLUORESCENCE DETECTION  

Microsoft Academic Search

In this study, the separation properties of alizarin, purpurin, carmine and morin were explored using capillary electrophoresis (CE). A 30 cm capillary (10 µm i.d.) and an applied voltage of 16-20 kV was used to separate the dyes prior to post-column detection in a sheath flow cuvette using laser-induced fluorescence (LIF). Two lasers were used for excitation; a 488 nm argon ion laser and

Douglas M. Goltz; Shokoufeh Ahmadi; Ghodrattolah Absalan; Douglas B. Craig

2012-01-01

424

Soot temperature measurements and implications for time-resolved laser-induced incandescence (TIRE-LII)  

Microsoft Academic Search

Emission spectroscopy has been used to determine soot particle temperatures in an ethene diffusion flame both under normal combustion conditions and also after irradiation with an intense laser pulse. On the basis of these measurements, a check on the models and an improvement of parameters underlying time-resolved laser-induced incandescence (TIRE-LII) was performed. With this technique a two-dimensionally resolved measurement of

Stephan Schraml; Stefan Dankers; Katharina Bader; Stefan Will; Alfred Leipertz

2000-01-01

425

Rapid in-situ analysis of liquid steel by laser-induced breakdown spectroscopy  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (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 allow a quantitative chemical analysis of the target material. LIBS is a fast, non-contact method allowing large working distances between the sample under investigation

J. Gruber; J. Heitz; H. Strasser; D. Bäuerle; N. Ramaseder

2001-01-01

426

Measurement of sputtered Mg particles in a plasma display panel discharge using laser induced fluorescence technique  

Microsoft Academic Search

Spatiotemporal distribution of Mg particles emitted from an MgO surface during an alternating current (ac) plasma display panel (PDP) discharge was directly measured using the laser induced fluorescence (LIF) technique. The results showed the existence of floating Mg particles intermittently emitted during short-lived PDP discharges. A spatial profile at 2 mm above the MgO surface had a peak at around

Youl-Moon Sung; Masahisa Otsubo; Chikahisa Honda

2006-01-01

427

Analysis of Minerals and Rocks by Laser-Induced Breakdown Spectroscopy  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) technique was applied for rapid analysis of major and minor elements composing geological samples including minerals, rocks, and a soil sample. The plasma was produced in air at atmospheric pressure by focusing on the targets a pulsed infrared Nd:YAG laser in open-path configuration. The emitted light in the UV-Vis was analyzed by a compact LIBS system

Diego M. Díaz Pace; Norberto A. Gabriele; Mayra Garcimuño; Cristian A. D'Angelo; Graciela Bertuccelli; Daniela Bertuccelli

2011-01-01

428

Temperature measurements of binary droplets using three-color laser-induced fluorescence  

Microsoft Academic Search

Evaporation of multicomponent droplets is a critical problem in many engineering applications, for example spray combustion. Knowledge of droplet temperature is a key issue in understanding the highly complex heat and mass-transfer phenomena related to multicomponent droplet evaporation and combustion. In this work, optical diagnosis based on three color-laser-induced fluorescence was developed: the objective was to measure the temperature of

C. Maqua; G. Castanet; Fabrice Lemoine; N. Doué; G. Lavergne

2006-01-01

429

Two-color laser-induced fluorescent thermometry for microfluidic systems  

Microsoft Academic Search

The feasibility of implementing a two-color laser-induced fluorescence (LIF) technique to study thermal transport at the microscale is investigated. Temperature-sensitive (Rhodamine B) and temperature-insensitive (Sulforhodamine-101) fluorescent dyes are used in tandem to determine fluid temperature with high accuracy and low noise using a pulsed Nd:YAG laser as an illumination source. While the fluorescence intensity of the temperature-sensitive dye is proportional

V K Natrajan; K T Christensen

2009-01-01

430

Use of capillary electrophoresis and laser-induced fluorescence for attomole detection of amino acids  

Microsoft Academic Search

A capillary electrophoresis and laser-induced fluorescence (CE–LIF) method was developed to identify and quantitate at amol (10?18) concentration. Amino acids were derivatized with 3-(4-carboxybenzoyl)-2-quinoline-carboxaldehyde prior to CE–LIF analysis. The assay was developed by varying the sodium borate concentration, buffer pH, operating voltage, and operating temperature. A run buffer system containing 6.25 mM borate, 150 mM sodium dodecyl sulfate, and 10

M Ummadi; B. C Weimer

2002-01-01

431

Trace detection of NO and NO 2 by photoionization and laser induced fluorescence techniques  

Microsoft Academic Search

The analytical capabilities of photoionization spectroscopy (PIS) and laser induced fluorescence (LIF) techniques have been evaluated to determine the relative merits of each technique for measurements of NO and NO2 at the ppb and sub-ppb level. For both techniques, excitation is accomplished via the A–X (1,0) band of NO near 215nm. For the ionization measurements, a (1+1) PIS scheme is

J. B. Simeonsson; S. A. Elwood; M. Niebes; R. Carter; A. Peck

1999-01-01

432

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

433

Remote detection of polynuclear aromatic hydrocarbons using laser-induced fluorescence. Interim report January 82-August 84  

SciTech Connect

This publication discusses the feasibility of remotely detecting gas-phase polynuclear aromatic hydrocarbons (PAHs) that might be produced during the combustion of propellant, explosive, and pyrotechnic (PEP) materials. Laboratory scale and remote laser-induced fluorescence measurements are presented.

Loda, R.T.

1985-01-01

434

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

435

Spatial Dosimetry with Violet Diode Laser-Induced Fluorescence of Water-Equivalent Radio-Fluorogenic Gels.  

E-print Network

??The following work describes investigations of spatial dosimetry using laser-induced fluorescence of a radio-fluorogenic detector embedded within water-equivalent media. The chemical composition of a gelatin-based… (more)

Sandwall, Peter A, II

2014-01-01

436

Modal analysis and damage detection by Fiber Bragg grating sensors  

Microsoft Academic Search

Damage detection and localization are critical issues for structural health monitoring. To this aim, many techniques have been proposed relating, the presence of damage to variations of its dynamic features between the undamaged and damaged states. Since a greater information content is localized at higher frequencies, sensing systems with adequate bandwidth and resolution are required. Here, Fiber Bragg grating sensors

P. Capoluongo; C. Ambrosino; S. Campopiano; A. Cutolo; M. Giordano; I. Bovio; L. Lecce; A. Cusano

2007-01-01

437

Application Prospects and Microstructural Features in Laser-Induced Rapidly Solidified High-Entropy Alloys  

NASA Astrophysics Data System (ADS)

Recently, high-entropy alloys (HEAs) have attracted much interest in the materials community, as they offer massive opportunities to observe new phenomena, explore new structure, and develop new materials. Particularly, it is attractive to prepare high-performance HEA coatings by laser-induced rapid solidification, which can be formed on the surface of components and parts in a variety of sizes and shapes with a lower cost in comparison with those bulk material fabrication methods. From the technical point of view, laser-induced rapid solidification could hamper the compositional segregation, improve the solubility in solid-solution phases, and lead to the strengthening effect by the grain refinement. This article reviews the recent work on the typical microstructural features and the mechanical and chemical properties in laser-induced rapidly solidified HEAs, and these data are compared with conventional Co- and Ni-based alloy coatings. The article concludes with suggestions for future research and development in HEAs, from considerations of their characteristic properties.

Zhang, Hui; Pan, Ye; He, Yi-Zhu; Wu, Ji-Li; Yue, T. M.; Guo, Sheng

2014-06-01

438

A combined laser-induced breakdown and Raman spectroscopy Echelle system for elemental and molecular microanalysis  

NASA Astrophysics Data System (ADS)

Raman and laser-induced breakdown spectroscopy is integrated into a single system for molecular and elemental microanalyses. Both analyses are performed on the same ~ 0.002 mm 2 sample spot allowing the assessment of sample heterogeneity on a micrometric scale through mapping and scanning. The core of the spectrometer system is a novel high resolution dual arm Echelle spectrograph utilized for both techniques. In contrast to scanning Raman spectroscopy systems, the Echelle-Raman spectrograph provides a high resolution spectrum in a broad spectral range of 200-6000 cm - 1 without moving the dispersive element. The system displays comparable or better sensitivity and spectral resolution in comparison to a state-of-the-art scanning Raman microscope and allows short analysis times for both Raman and laser induced breakdown spectroscopy. The laser-induced breakdown spectroscopy performance of the system is characterized by ppm detection limits, high spectral resolving power (15,000), and broad spectral range (