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1

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

SciTech Connect

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

Pennington, D.M.

1992-04-01

2

Femtosecond laser-induced periodic structure adjustments based on electron dynamics control: from subwavelength ripples to double-grating structures.  

PubMed

This study proposes a method for adjusting subwavelength ripple periods and the corresponding double-grating structures formed on fused silica by designing femtosecond laser pulse trains based on localized transient electron density control. Four near-constant period ranges of 190-490 nm of ripples perpendicular to the polarization are obtained by designing pulse trains to excite and modulate the surface plasmon waves. In the period range of 350-490 nm, the double-grating structure is fabricated in one step, which is probably attributable to the grating-assisted enhanced energy deposition and subsequent thermal effects. PMID:24081041

Shi, Xuesong; Jiang, Lan; Li, Xin; Wang, Sumei; Yuan, Yanping; Lu, Yongfeng

2013-10-01

3

Maskless Fabrication of High Quality DFB Laser Gratings by Laser Induced Chemical Etching  

Microsoft Academic Search

High quality submicron DFB laser gratings with 130 nm groove depth are fabricated without roughness on a grating surface by laser induced chemical etching. It is found that rigid configuration of an irradiation cell and directional etching performance of laser etching is very important to obtain high quality gratings.

Yoshinobu Aoyagi; Satoshi Masuda; Atsutoshi Doi; Susumu Namba

1985-01-01

4

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

SciTech Connect

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

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

1995-07-11

5

Laser-induced grating measurements of energy migration in Tm,Ho:YAG  

Microsoft Academic Search

What may be the first direct measurement of spatial energy migration among the Tm(3+) ions in a Tm,Ho:YAG crystal at room temperature is reported. Four-wave mixing techniques were used to establish and probe transient laser-induced population gratings in the Tm(3+) ions. The grating decay rate was measured as a function of the grating spacing. The results show the presence of

Valentina A. French; Richard C. Powell

1991-01-01

6

Observation of ? in a flame by two-colour laser-induced-grating spectroscopy  

NASA Astrophysics Data System (ADS)

By using two-colour laser-induced-grating spectroscopy (TC-LIGS), we observed the third-overtone spectrum of the O - H stretch of water vapour at a point in a stoichiometric 0957-0233/8/8/013/img2 - air flame. We also demonstrated the extension of these point measurements to a line image in a flame. Only thermal gratings could be observed. The reasons for this and the difficulties in making a practical combustion diagnostic are discussed.

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

1997-08-01

7

Subpicosecond-relaxation studies using tunable-laser-induced-grating techniques  

NASA Astrophysics Data System (ADS)

Tunable Laser induced Grating spectroscopy, a type of variable-frequency four-wave-mixing, provides a new and useful approach for the study of ultrafast processes in the frequency domain, with potential application to the measurement of timescales as short as a few femtoseconds. This work examines in detail the Tunable-Laser-Induced-Grating lineshape for excited-state gratings, including saturation effects, using a two-step iterative solution to the rate equations for an n-level system. Lineshapes for phase gratings, also, including those due to the optical Kerr effect, are reviewed. An optically induced grating in an arbitrary material is shown to exhibit a lineshape proportional to the Fourier transform of the material impulse response. The choice of beam geometry is discussed, and simple explicit expression for the Bragg angles in the general three dimensional, nondegenerate four-wave-mixing problem are derived. Previous theoretical and experimental work on the optical-Kerr liquid, carbon disulfide, and the organic dye, malachite green, is summarized, and the results of Tunable-Laser-Induced-Grating experiments using a geometry employing two input frequencies are presented.

Trebino, F. P.

1983-01-01

8

Laser induced photoacoustic grating effects in molecular crystals  

Microsoft Academic Search

A transient grating of singlet electronic excited states is produced in a pentacene-doped p-terphenyl molecular crystal by optical absorption from two crossed time-coincident picosecond excitation pulses at 532 nm. The diffraction properties of this volume grating are probed by a weak, variably delayed, Bragg-matched picosecond probe pulse. At high excitation intensities, a strong oscillatory behavior in the time-dependent scattering efficiency

J. R. Salcedo; A. E. Siegman

1979-01-01

9

Laser-Induced Grating Spectroscopy of Alexandrite Crystals,  

National Technical Information Service (NTIS)

Four-wave-mixing techniques were used to establish and probe population gratings of Chromium ions in alexandrite crystals at temperatures between 10 and 300 K. The results were interpreted in terms of the interaction of the laser radiation with a two-leve...

G. D. Gilliland A. Suchocki K. W. Ver Steeg R. Powell

1988-01-01

10

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

NASA Astrophysics Data System (ADS)

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

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

2008-10-01

11

Nonlinear dynamic of IR laser-induced surface processes  

Microsoft Academic Search

This paper deals with the problems of dynamics of laser(IR)-induced surface processes. It refers somewhat to laser-induced gas-phase processes near a solid surface and processes of adsorption and desorption in the frame at nonequilibrium thermodynamics. The main attention is devoted to the processes of laser-induced structure formation (metal oxidation) based on pure thermal effects of laser light, both in the

L. Nànai; R. Vajtai; T. F. George

1995-01-01

12

Time resolved laser-induced plasma dynamics  

Microsoft Academic Search

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 800nm), 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

Xianglei Mao; Sy-Bor Wen; Richard E. Russo

2007-01-01

13

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

14

Laser-induced grating spectroscopy of highly excited overtone and combination vibrational states of methane  

NASA Astrophysics Data System (ADS)

Laser-induced grating spectroscopy is applied to investigate weak overtone and combination absorption bands of methane. The rotationally-resolved spectra of transitions to the polyads Pn, n = 8-10, 12 recorded at pressures ranging from 0.2 to 4 bar and temperatures 298 K and 124-130 K cover a broad interval between 891 and 618 nm (11 220-16 180 cm-1) and contain a significant amount of prominent narrow lines which correspond to stationary rovibrational states. The absorption cross sections of the weakest detected methane transitions are estimated to be as small as ?10-26 cm2 molecule-1. The technique is suitable to provide data for the development and verification of new models describing the complex energy structure of highly vibrationally excited molecules.

Kozlov, D. N.; Sadovskii, D. A.; Radi, P. P.

2013-09-01

15

Diagnostics of water-containing gas mixtures using thermal laser-induced gratings  

NASA Astrophysics Data System (ADS)

Laser-induced gratings (LIGs) experiments, employing vibrational-overtone excitation of H2O molecules through rovibrational transitions of the (2 1 1) ? (0 0 0) band around 820 nm to produce gratings, have been performed in humid ambient air, in a room-temperature cell with neat water vapor or that diluted in buffer gas at pressures of 0.02 4 bar, and in the vicinity of premixed atmospheric pressure CH4-air flame, with the aim to investigate the feasibilities of the techniques for accomplishing gas diagnostics or tracing H2O at various temperatures and pressures. In highly vibrationally-excited H2O rapid multi-stage collisional thermalization processes occur, and as a result both strong oscillatory (due to standing acoustic waves) and stationary (due to stationary density modulations) contributions to LIGs have been observed in gas mixtures. Temporal profiles of LIG signals recorded at various conditions of gas mixtures employed have been analysed in frame of a model of a two- or three-stage R T, V V?, and V T collisional relaxation of H2O and buffer gas molecules. The informative parameters, like adiabatic sound velocity, gas temperature, H2O mole fraction have been derived. The results of the analysis are presented, demonstrating possibilities and challenges of the technique in application to gas diagnostics.

Hemmerling, B.; Kozlov, D. N.; Stel'Makh, O. M.; Attal-Trétout, B.

2006-01-01

16

Observation of beating between cw lasers by time-delayed laser-induced double gratings mediated by photorefractive effect  

Microsoft Academic Search

We have demonstrated in KNbO3:Fe that the time-delayed laser-induced double gratings mediated by photorefractive effect can be employed to measure the frequency difference between two cw light sources. Due to the highly sensitive photorefractive effect in KNbO3:Fe the power of the incident beams can be less than 1 mW. With this technique, we have observed beating between the blue (488

Xuezhou Ding; Zhiguo Zhang; Qian Jiang; Xin Mi; Zuhe Yu; Panming Fu; Dezhong Shen; Xiaoyan Ma

1994-01-01

17

Measurements of mean and fluctuating temperature in an underexpanded jet using electrostrictive laser-induced gratings  

NASA Astrophysics Data System (ADS)

Instantaneous temperature measurements were obtained in an underexpanded jet using electrostrictive laser-induced gratings. Evaluation of the technique under static, low-pressure conditions provided a baseline uncertainty or precision for single-shot temperature measurements of 4.4% of the local mean temperature, which represents the minimum detectable temperature fluctuation. The underexpanded jet was operated at a nozzle pressure ratio of 2.39 and a fully expanded jet Mach number of 1.19. Data were acquired along the centerline and over two radial traverses through the shear layer. Mean temperature data agree well with expectations, describing the shock-cell structure and the compressible shear layer. The growth in shear-layer width with downstream distance can be identified in the mean and fluctuating temperature measurements. Temperature fluctuations are near the baseline detection limit in the jet core and surrounding ambient air, and reach a maximum in the shear layer. The temperature fluctuation measurements compare well with previous computational and experimental work, confirming the application of the technique to a turbulent, supersonic flow.

Kuehner, Joel P.; Tessier, F. Andrew; Kisoma, Allan; Flittner, Jonathan G.; McErlean, Michael R.

2010-03-01

18

Measurement of the thermal diffusivity and speed of sound of hydrothermal solutions via the laser-induced grating technique  

SciTech Connect

We use the laser-induced grating technique to measure the thermal diffusivity and speed of sound of hydrothermal solutions. In this noninvasive optical techniques, a transient gradient is produced in the hydrothermal solution by optical absorption from two crossed, time-coincident nanosecond laser pulses. The grating is probed by measuring the diffraction efficiency of a third laser beam. The grating relaxes via thermal diffusion, and the thermal diffusivity is determined by measuring the decay of the grating diffraction efficiency as a function of the pump-probe delay time. In addition, intense pump pulses produce counterpropagating acoustic waves that appear as large undulations in the transient grating decay spectrum. The speed of sound in the sample is simply the grating fringe spacing divided by the undulation period. The cell is made from a commercial high-pressure fitting and is equipped with two diamond windows for optical access. Results are presented for dilute dye/water solutions with T = 400{degrees}C and pressures between 20 and 70 MPa.

Butenhoff, T.J. [Los Alamos National Lab., NM (United States)

1995-01-01

19

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

PubMed

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

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

2011-06-10

20

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

21

Observation of beating between cw lasers by time-delayed laser-induced double gratings mediated by photorefractive effect  

NASA Astrophysics Data System (ADS)

We have demonstrated in KNbO3:Fe that the time-delayed laser-induced double gratings mediated by photorefractive effect can be employed to measure the frequency difference between two cw light sources. Due to the highly sensitive photorefractive effect in KNbO3:Fe the power of the incident beams can be less than 1 mW. With this technique, we have observed beating between the blue (488 nm) and the green (514.5 nm) lines of an argon ion laser, which shows a beat note of 31.2 fs period.

Ding, Xuezhou; Zhang, Zhiguo; Jiang, Qian; Mi, Xin; Yu, Zuhe; Fu, Panming; Shen, Dezhong; Ma, Xiaoyan

1994-11-01

22

Dynamics of Laser-Induced Cavitation Bubble near Solid Boundary  

NASA Astrophysics Data System (ADS)

The dynamics of a laser-induced cavitation bubble created near solid boundary is investigated using a new force sensor together with a hydrophone. The experimental results indicate that liquid-jet formation and acoustic transient emission are general features of bubble dynamics; liquid-jet formation occurs earlier than that of the acoustic transient. A comparison of the liquid jet energy and acoustic energy reveals that the acoustic transient, rather than the liquid jet, plays a vital role in the damping mechanism during the second collapse for ?=0.75 (?=L/Rmax, where Rmax being the maximum bubble radius and L denoting the distance of the cavity inception from the boundary); moreover, the amplitudes of acoustic transients and liquid jet versus the nondimensional distance ? are also derived, which are valuable in hydraulic cavitation, laser lithotripsy and laser ophthalmology.

Zhao, Rui; Liang, Zhong-cheng; Xu, Rong-qing; Lu, Jian; Ni, Xiao-wu

2008-07-01

23

Review of femtosecond infrared laser-induced fibre Bragg grating sensors made with a phase mask  

Microsoft Academic Search

Purpose – The purpose of this paper is to present a review of research performed at the Communications Research Centre Canada on sensing applications of femtosecond infrared laser-inscribed Bragg gratings. Design\\/methodology\\/approach – By using fibre Bragg gratings induced with ultrafast infrared radiation, inscription of high temperature stable sensors in standard and exotic optical waveguides is investigated for a variety of

Stephen J. Mihailov; Dan Grobnic; Christopher W. Smelser; Robert B. Walker; Ping Lu; Huimin Ding

2011-01-01

24

Relationship between laser-induced gratings and vibrational properties of Eu-doped glasses  

SciTech Connect

Four-wave-mixing techniques have been shown previously to produce permanent refractive index gratings in Eu-doped glasses by resonant excitation of the Eu/sup 3+/ ions. A variety of glass hosts were studied and it was found that permanent holographic gratings could be established in some of these but not in others. We report here an extension of our previous work which includes investigations of new materials, attempts to form gratings with different excitation wavelengths, and a comparison of the Raman and resonant Raman spectra of glasses which do and do not exhibit permanent holographic gratings. It was found that direct excitation into the /sup 5/D/sub 0/ level did not produce permanent gratings. It was also found that glasses which do exhibit permanent gratings have high-frequency vibrational modes which couple strongly to the Eu/sup 3+/ ions. These results help to verify the model proposed previously to explain the origin of the holographic grating in terms of structural changes caused by thermal effects arising from radiationless relaxation through high-frequency local modes.

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

1987-03-15

25

Investigation of fs-laser induced damage on high reflection mirrors used for 800 nm broadband pulse compression gratings  

NASA Astrophysics Data System (ADS)

High reflection mirror for 800 nm broadband pulse compression grating was fabricated by electron beam evaporation using three dielectrics (Ta2O5/SiO2/HfO2). It has more than 99% reflectance with bandwidth larger than 160 nm around wavelength of 800 nm and 84.3% transmission at the exposure wavelength of 413 nm. Laser-induced damage behaviors of the mirror were investigated by 800 nm TE polarization laser with pulse width ?p of 40-100 fs. The laser damage threshold of the mirror observes a fitting scaling law of ?p0.29. The damage characters and near field distribution consistently indicated that the initial damage of the mirror was ascribed to nonlinear ionization in the zone position of electric field intensity maximum. The experimental threshold can be fitted with a model based on electron production taking into account photoionization and avalanche ionization. The mirrors with good spectral properties and high laser damage threshold provide a solid base for fabricating 800 nm pulse compression gratings.

Kong, Fanyu; Chen, Shunli; Jin, Yunxia; Liu, Shijie; Guan, Heyuan; Du, Ying; He, Hongbo

2013-12-01

26

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

27

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

SciTech Connect

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

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

2002-04-30

28

Experimental investigation of laser-induced bubble dynamics near elastic/soft material in distilled water  

NASA Astrophysics Data System (ADS)

This study deals with an experimental investigation of the dynamics of laser-induced single bubble near the rigid material plate and near the elastic/soft material plate in the distilled water at room temperature under atmospheric pressure. A pulsed Nd:YAG laser was focused into the distilled water to make plasma and single bubble. The bubble repeated expanding and shrinking motion several times, and then collapsed. This behavior occurred on the sub-millisecond timescale. The solid wall near the bubble makes an asymmetric flow field. Many experiments on the behavior of laser-induced bubble near the rigid material have been reported. The bubble near the solid wall moves toward the rigid wall during its shrinking and rebounding process. The behavior of laser-induced bubble near the soft material, however, has not been well clarified. The soft material such as body tissue can deform and influence the behavior of the laser-induced bubble. Since the high peak power laser has been applied in the field of bioengineering and medical treatment, it is of great importance to clarify the effect of the soft material near the laser-induced cavitation bubble. In this research the behavior of laser-induced bubble near the elastic/soft material was visualized with schlieren method and investigated.

Nakajima, S.; Yamamoto, Y.; Ota, M.; Maeno, K.

2009-02-01

29

Dynamics of laser-induced cavitation in liquid  

NASA Astrophysics Data System (ADS)

This paper presents an analysis of the rate of bubble expansion and an estimate of maximum bubble diameter and bubble lifetime prior to collapse. Such data are needed for the optimization of system parameters for elemental analysis in water by laser-induced breakdown spectroscopy (LIBS). Two techniques were used for this study: pump-probe beam deflection and high-speed photography. Plasma in the water bulk was generated by a focussed laser pulse with energy of 140 mJ and pulse duration of 10 ns, operating at the fundamental Nd:YAG laser wavelength (1064 nm). Reasonable agreement on the value of maximum bubble diameter was obtained between the photographic and probe beam deflection results. Reasonable agreement for the total duration of the oscillating cavitation bubble was also obtained for the two techniques, with a mean value of ˜800 ?s. A comparison between empirical results and predictions based on the Rayleigh equation is also presented.

Peel, Christopher S.; Fang, Xiao; Ahmad, S. Rafi

2011-06-01

30

Role of Bulk Vaporization in the Dynamics of Laser-Induced Erosion Plumes of Metals  

Microsoft Academic Search

In different regimes of exposure of metals to pulsed laser radiation, we show the role played by the liquid-drop phase formed from the target material in a laser-induced erosion plume due to bulk vaporization, in the dynamics of this plume. For some metals, the ranges of power densities of the acting laser radiation, at which the condensed-phase particles influence the

V. K. Goncharov; A. F. Chernavskii

2004-01-01

31

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

Microsoft Academic Search

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

S. C. Jiang; X. X. Zhang

2005-01-01

32

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

33

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

34

Dynamics of femtosecond laser-induced melting of silver  

SciTech Connect

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

Chan Wailun; Averback, Robert S.; Cahill, David G. [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Lagoutchev, Alexei [School of Chemical Science, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

2008-12-01

35

Dynamics of laser induced micro bubble clusters on tissue phantoms  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

36

Molecular dynamics studies of ultrafast laser-induced nonthermal melting  

NASA Astrophysics Data System (ADS)

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

Wang, Y.; Xu, X.

2013-03-01

37

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

38

Photodissociation and reaction dynamics of vibrationally excited molecules. Technical progress report, 1993--1994.  

National Technical Information Service (NTIS)

Combined vibrational overtone excitation and laser induced fluorescence detection was used to study dissociation dynamics of hydroxylamine (NH(sub 2)OH), laser induced grating experiments on water were analyzed, discovering the important role that electro...

1994-01-01

39

Micro Dynamics of Pulsed Laser Induced Bubbles in Dusty Plasma Liquids  

NASA Astrophysics Data System (ADS)

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

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

2008-09-01

40

Self-packaged Type II femtosecond IR laser induced fiber Bragg grating for temperature applications up to 1000 °C  

NASA Astrophysics Data System (ADS)

We propose a thermally stable Type II grating made with ultrafast infrared radiation in a silica-based 400 ?m clad single mode fiber cane as a self packaged grating due to its ability to maintain good mechanical integrity after more 100 hours at 1000°C.

Grobnic, Dan; Mihailov, Stephen J.; Walker, Robert B.; Smelser, Christopher W.

2011-05-01

41

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

42

Structural and magnetic dynamics of a laser induced phase transition in FeRh.  

PubMed

We use time-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (?(1)~30 ps). This is significantly faster than the magnetic response (?(2)~60 ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases coexist on short time scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented. PMID:22463562

Mariager, S O; Pressacco, F; Ingold, G; Caviezel, A; Möhr-Vorobeva, E; Beaud, P; Johnson, S L; Milne, C J; Mancini, E; Moyerman, S; Fullerton, E E; Feidenhans'l, R; Back, C H; Quitmann, C

2012-02-21

43

Structural and Magnetic Dynamics of a Laser Induced Phase Transition in FeRh  

NASA Astrophysics Data System (ADS)

We use time-resolved x-ray diffraction and magneto-optical Kerr effect to study the laser-induced antiferromagnetic to ferromagnetic phase transition in FeRh. The structural response is given by the nucleation of independent ferromagnetic domains (?1˜30ps). This is significantly faster than the magnetic response (?2˜60ps) given by the subsequent domain realignment. X-ray diffraction shows that the two phases coexist on short time scales and that the phase transition is limited by the speed of sound. A nucleation model describing both the structural and magnetic dynamics is presented.

Mariager, S. O.; Pressacco, F.; Ingold, G.; Caviezel, A.; Möhr-Vorobeva, E.; Beaud, P.; Johnson, S. L.; Milne, C. J.; Mancini, E.; Moyerman, S.; Fullerton, E. E.; Feidenhans'L, R.; Back, C. H.; Quitmann, C.

2012-02-01

44

Experimental investigation of new concentration measurements using nonlinear dynamics through laser-induced thermal lens oscillation  

NASA Astrophysics Data System (ADS)

The laser-induced thermal lens oscillation that is generated in an organic solution by Ar-ion laser irradiation was studied as a nonlinear dynamic system. The different dynamic states power (P), depth (d) from a surface to a laser beam position, and solvent concentration. The transitions of dynamic states including several complicated states, for example, periodic, double periodic, were investigated by varying the parameters (P, d) for 27%, 30%, and 33% of tri-n-butyl phosphate solution diluted with n-dodecane. It was found that these transitions were strongly dependent on the concentration of the TBP solution. Based on this result, we also propose an application to solvent concentration measurement with a difference of 3%.

Todoriki, Masaru; Suzuki, Atsuyuki

1996-06-01

45

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

46

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

Microsoft Academic Search

This paper studies gratings engraved in a multilayer dielectric stack for ultra high intensity laser compressors. A metal layer is inserted between the substrate and the dielectric stack to reduce the number of dielectric bilayers and thus the mechanical stress within the stack. A code taking account the fluctuation range of the geometrical parameters during the fabrication process is used

Nicolas Bonod; Jérôme Néauport

2006-01-01

47

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

48

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

49

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

NASA Astrophysics Data System (ADS)

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

Bandrauk, Andre D.; Paramonov, Guennaddi

2012-03-01

50

Observation of narrowband intrinsic spectra of Brillouin dynamic gratings.  

PubMed

We experimentally demonstrate that the reflection spectrum of a Brillouin dynamic grating in a polarization-maintaining fiber can be much narrower than the intrinsic linewidth of the stimulated Brillouin scattering, matching well with the theory of a fiber Bragg grating in terms of the linewidth and the reflectivity. A 3 dB bandwidth as narrow as 10.5 MHz is observed with the Brillouin dynamic grating generated in a 9 m uniform fiber. PMID:20808382

Song, Kwang Yong; Yoon, Hyuk Jin

2010-09-01

51

Resolving the genuine laser-induced ultrafast dynamics of exchange interaction in ferromagnet/antiferromagnet bilayers  

NASA Astrophysics Data System (ADS)

The response of exchange coupled ferromagnet/antiferromagnet metallic bilayers to laser excitation down to the femtosecond time scale is investigated. Differently from previous attempts, the ultrafast dynamics of exchange interaction is deduced by carefully analyzing precessional transients of the ferromagnetic magnetization, measured by means of time-resolved magneto-optical Kerr effect, rather than by monitoring changes in the hysteresis loop as a function of pump-probe delay. Thereby we are able to estimate the characteristic time scale of laser-induced exchange-bias quenching in a polycrystalline Co/IrMn bilayer, ?EB,0=(0.7±0.5)ps . The fast decrease in exchange coupling upon laser heating is attributed to a spin disorder at the interface created by laser heating.

Dalla Longa, F.; Kohlhepp, J. T.; de Jonge, W. J. M.; Koopmans, B.

2010-03-01

52

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

PubMed

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

Lin, C D; Xu, Junliang

2012-10-14

53

Dynamic strain measurements by fibre Bragg grating sensor  

Microsoft Academic Search

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

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

2004-01-01

54

Dynamics of laser-induced cavitation bubbles near an elastic boundary used as a tissue phantom  

NASA Astrophysics Data System (ADS)

The behavior of a laser-produced cavitation bubble near an elastic boundary as well as the deformation of the boundary induced by bubble motion are investigated by means of high-speed photography and acoustic measurements. The elastic boundary, used as a tissue phantom, consists of a polyacrylamide (PAA) gel whose elastic properties can be controlled, by modifying the water content of the sample, to mimic various biological tissues. The bubble dynamics is strongly dependent on the dimensionless distance ?=s/Rmax between bubble and boundary and on the elastic properties of the boundary. For example, in the case of a PAA gel with 80% water concentration, the general features of the bubble dynamics are, for ?>0.8, bubble migration and jet formation directed away from the boundary, for 0.8>?>0.2, formation of a mushroom-like shape of the bubble during collapse, bubble splitting and penetration of a re-entrant liquid jet into the boundary while, for ?<0.52, jet formation of PAA-material directed away from the elastic boundary occurs. The latter phenomenon can be used to enhance the efficiency of laser-induced tissue ablation. .

Brujan, Emil-Alexandru; Nahen, Kester; Schmidt, Peter; Vogel, Alfred

2000-07-01

55

Dynamics of laser-induced cavitation bubbles near an elastic boundary  

NASA Astrophysics Data System (ADS)

The interaction of a laser-induced cavitation bubble with an elastic boundary and its dependence on the distance between bubble and boundary are investigated experimentally. The elastic boundary consists of a transparent polyacrylamide (PAA) gel with 80% water concentration with elastic modulus E = 0.25 MPa. At this E-value, the deformation and rebound of the boundary is very pronounced providing particularly interesting features of bubble dynamics. It is shown by means of high-speed photography with up to 5 million frames s[minus sign]1 that bubble splitting, formation of liquid jets away from and towards the boundary, and jet-like ejection of the boundary material into the liquid are the main features of this interaction. The maximum liquid jet velocity measured was 960 m s[minus sign]1. Such high-velocity jets penetrate the elastic boundary even through a water layer of 0.35 mm thickness. The jetting behaviour arises from the interaction between the counteracting forces induced by the rebound of the elastic boundary and the Bjerknes attraction force towards the boundary. General principles of the formation of annular and axial jets are discussed which allow the interpretation of the complex dynamics. The concept of the Kelvin impulse is examined with regard to bubble migration and jet formation. The results are discussed with respect to cavitation erosion, collateral damage in laser surgery, and cavitation-mediated enhancement of pulsed laser ablation of tissue.

Brujan, Emil-Alexandru; Nahen, Kester; Schmidt, Peter; Vogel, Alfred

2001-04-01

56

Study of collisional deactivation of O2( b 1?{/g +}) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings  

NASA Astrophysics Data System (ADS)

Collisional deactivation of O2( b 1?{/g +}) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H2/O2 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 1?{/g +} state of O2 molecules deactivation rates are measured in a 4.3 vol % H2 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 H2 with O2( b 1?{/g +}) and O2( a 1? g ) up to temperatures of 780-790 K at time delays up to 10 ?s after the excitation pulse. The parameters of the obtained temperature dependence of the ( b 1?{/g +} 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 H2O molecules which appear as the mixture, as the result of the dark gross reaction with O2 molecules in the ground state, O2 + 2H2 ? 2H2O. The measurements show that this reaction results in complete transformation of H2 into H2O at temperatures of 790-810 K.

Kozlov, D. N.; Kobtsev, V. D.; Stel'makh, O. M.; Smirnov, V. V.

2013-07-01

57

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

58

Laser-Induced Thermal Acoustics  

Microsoft Academic Search

Laser-induced thermal acoustics (LITA) is a new technique for remote nonintrusive measurement of thermophysical gas properties. LITA involves forming, via opto-acoustic effects, grating-shaped perturbations of gas properties by the use of intersecting beams from a short-pulse laser. A third beam scatters coherently into a signal beam off the perturbation grating via acousto-optical effects. The evolution of the gas perturbations modulates

Eric Bryant Cummings

1995-01-01

59

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

NASA Astrophysics Data System (ADS)

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

Chen, Yen-Hung; I, Lin

2008-02-01

60

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

SciTech Connect

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

Wu, Benny

2012-04-05

61

Dynamics of laser-induced cavitation bubbles near an elastic boundary  

Microsoft Academic Search

The interaction of a laser-induced cavitation bubble with an elastic boundary and its dependence on the distance between bubble and boundary are investigated ex- perimentally. The elastic boundary consists of a transparent polyacrylamide (PAA) gel with 80% water concentration with elastic modulus E =0 :25 MPa. At this E- value, the deformation and rebound of the boundary is very pronounced

PETER S CHMIDT; ALFRED V OGEL

2001-01-01

62

Dynamic strain measurement with a fibre Bragg grating sensor system  

Microsoft Academic Search

In this paper a fibre Bragg grating measuring system is presented to detect dynamic seismic signals in underground structures, rock mass and bridges, etc. To improve the sensitivity of dynamic strain measurement the wavelength of the used DFB-laser is automatically optimised by the actual dc photovoltage measurement. A strain calculation method is given. An adaptive filtering algorithm is proposed and

J.-G. Liu; C. Schmidt-Hattenberger; G. Borm

2002-01-01

63

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

PubMed

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

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

2011-01-28

64

Variable delay using stationary and localized Brillouin dynamic gratings  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

65

Dynamics of laser-induced cavitation bubbles near an elastic boundary  

Microsoft Academic Search

The interaction of a laser-induced cavitation bubble with an elastic boundary and its dependence on the distance between bubble and boundary are investigated experimentally. The elastic boundary consists of a transparent polyacrylamide (PAA) gel with 80% water concentration with elastic modulus E = 0.25 MPa. At this E-value, the deformation and rebound of the boundary is very pronounced providing particularly

Emil-Alexandru Brujan; Kester Nahen; Peter Schmidt; Alfred Vogel

2001-01-01

66

Dynamics of laser-induced cavitation bubbles near elastic boundaries: influence of the elastic modulus  

Microsoft Academic Search

The interaction of a laser-induced cavitation bubble with an elastic boundary is investigated experimentally by high-speed photography and acoustic measurements. The elastic material consists of a polyacrylamide (PAA) gel whose elastic properties can be controlled by modifying the water content of the sample. The elastic modulus, E, is varied between 0.017 MPa and 2.03 MPa, and the dimensionless bubble boundary

Emil-Alexandru Brujan; Kester Nahen; Peter Schmidt; Alfred Vogel

2001-01-01

67

Dynamics of laser-induced cavitation bubbles near elastic boundaries: influence of the elastic modulus  

Microsoft Academic Search

The interaction of a laser-induced cavitation bubble with an elastic boundary is investigated experimentally by high-speed photography and acoustic measurements. The elastic material consists of a polyacrylamide (PAA) gel whose elastic proper- ties can be controlled by modifying the water content of the sample. The elastic modulus, E, is varied between 0.017 MPa and 2.03 MPa, and the dimensionless bubble{boundary

PETER S CHMIDT; ALFRED V OGEL

2001-01-01

68

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

PubMed Central

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

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

2012-01-01

69

Influence of sample temperature on the expansion dynamics and the optical emission of laser-induced plasma  

NASA Astrophysics Data System (ADS)

We investigate the influence of sample temperature on the dynamics and optical emission of laser induced plasma for various solid materials. Bulk aluminum alloy, silicon wafer, and metallurgical slag samples are heated to temperature TS ? 500 °C and ablated in air by Nd:YAG laser pulses (wavelength 1064 nm, pulse duration approx. 7 ns). The plasma dynamics is investigated by fast time-resolved photography. For laser-induced breakdown spectroscopy (LIBS) the optical emission of plasma is measured by Echelle spectrometers in combination with intensified CCD cameras. For all sample materials the temporal evolution of plume size and broadband plasma emission vary systematically with TS. The size and brightness of expanding plumes increase at higher TS while the mean intensity remains independent of temperature. The intensity of emission lines increases with temperature for all samples. Plasma temperature and electron number density do not vary with TS. We apply the calibration-free LIBS method to determine the concentration of major oxides in slag and find good agreement to reference data up to TS = 450 °C. The LIBS analysis of multi-component materials at high temperature is of interest for technical applications, e.g. in industrial production processes.

Eschlböck-Fuchs, S.; Haslinger, M. J.; Hinterreiter, A.; Kolmhofer, P.; Huber, N.; Rössler, R.; Heitz, J.; Pedarnig, J. D.

2013-09-01

70

Time-resolved dynamics of laser-induced micro-jets from thin liquid films  

Microsoft Academic Search

Laser-induced forward transfer (LIFT) is a high-resolution direct-write technique, which can print a wide range of liquid\\u000a materials without a nozzle. In this process, a pulsed laser initiates the expulsion of a high-velocity micro-jet of fluid\\u000a from a thin donor film. LIFT involves a novel regime for impulsively driven free-surface jetting in that viscous forces developed\\u000a in the thin film

Matthew S. Brown; Nicholas T. Kattamis; Craig B. Arnold

2011-01-01

71

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

National Technical Information Service (NTIS)

The dynamic response of a fiber optic Bragg grating to mechanical vibrations is examined both theoretically and experimentally. The theoretical expressions describing the consequences of changes in the grating's reflection spectrum are derived for partial...

G. Adamovsky J. Lekki J. A. Lock

2002-01-01

72

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

73

All-optical signal processing using dynamic Brillouin gratings  

NASA Astrophysics Data System (ADS)

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.

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

2013-04-01

74

Observation of Brillouin dynamic grating in a photonic chip.  

PubMed

We report demonstration of a Brillouin dynamic grating (BDG) in a photonic chip. A BDG was characterized in a 6.5 cm long chalcogenide (As(2)S(3)) rib waveguide using CW pumps in x polarization and read using a CW probe in y polarization. The measured reflectivity, on-off ratio, and 3 dB bandwidth (f(3 dB)) for the BDG were 0.4%, ~28 dB, and ~6 GHz, respectively. PMID:23381419

Pant, Ravi; Li, Enbang; Poulton, Christopher G; Choi, Duk-Yong; Madden, Steve; Luther-Davies, Barry; Eggleton, Benjamin J

2013-02-01

75

Simulation of laser-induced coupled electron-nuclear dynamics and time-resolved harmonic spectra in complex systems  

NASA Astrophysics Data System (ADS)

We present a theoretical approach for the simulation of time-resolved harmonic spectra, including the effect of nuclear dynamics, which is applicable to complex systems involving many nuclear degrees of freedom. The method is based on the combination of our semiclassical field-induced surface hopping approach for the treatment of laser-induced nuclear dynamics with the time-dependent density functional theory for electron dynamics. We apply our method to the simulation of ultrafast nonadiabatic dynamics and time-resolved harmonic spectra in small silver clusters (Ag2 and Ag8), which exhibit discrete molecularlike electronic transitions. We demonstrate that the harmonic signal is highly sensitive to the nuclear dynamics and thus can be used as a probe of coupled electron-nuclear dynamics, which is complementary to common pump-probe methods such as time-resolved photoelectron spectroscopy. Our simulations allowed us also to determine the mechanism and the time scale of nonradiative relaxation in the “magic” Ag8 cluster and have provided a fundamental insight into ultrafast dynamics of metal nanoclusters in the size regime where “each atom counts.” The excited-state dynamics of Ag8 involves an isomerization process from the initial structure with Td symmetry to the quadratic antiprism structure with D4d symmetry which takes place on a time scale of ~600 fs and is clearly identified in a time-resolved harmonic signal. Our theoretical approach is generally applicable for the prediction of time-resolved harmonic spectra in complex systems with many nuclear degrees freedom and should serve to stimulate new ultrafast experiments utilizing harmonic signals as a probe for nonadiabatic processes in molecular systems.

Lisinetskaya, Polina G.; Mitri?, Roland

2011-03-01

76

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

NASA Astrophysics Data System (ADS)

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

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

1992-08-01

77

Dynamic self-enhanced diffraction from written photorefractive gratings  

NASA Astrophysics Data System (ADS)

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

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

2000-01-01

78

Novel interrogation system for dynamic strain measurement based on fiber Bragg grating sensor using long period grating pair and EDF  

Microsoft Academic Search

In this paper, we employ a novel demodulation scheme to monitor the dynamic perturbation of a fiber Bragg grating (FBG) sensor using an long-period grating (LPG) pair with erbium-doped fiber (EDF) inserted between the two LPGs. The experimental results show that the proposed technique features high resolution and much more immunity to temperature perturbation compared to the conventional unbalanced Mach-Zehnder

Jaehoon Jung; Yong Wook Lee; Byoungho Lee

2000-01-01

79

The characteristics of dynamic gratings in ultra-narrow linewidth erbium-doped fiber ring lasers  

NASA Astrophysics Data System (ADS)

The characteristics of dynamic gratings greatly affect the linewidth and mode hopping properties of ultra-narrow linewidth erbium-doped fiber lasers. In this paper, we propose a novel method to estimate the temporal evolution of the reflectance spectrum of the dynamic gratings recorded in EDF based on the transient effect of the erbium ions. An experimental setup is also proposed to measure the reflectivity spectrum of the dynamic gratings utilized in lasers. The experimental data are compared with the numerical results and their differences are analyzed. The experiment results reveal some important transient characteristics of dynamic gratings in real lasers which are helpful to understand the mechanism of mode hopping.

Xu, Pan; Hu, Zhengliang; Hu, Yongming; Ma, Mingxiang; Ma, Lina

2011-11-01

80

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

81

Dynamics of laser-induced cavitation bubbles near elastic boundaries: influence of the elastic modulus  

NASA Astrophysics Data System (ADS)

The interaction of a laser-induced cavitation bubble with an elastic boundary is investigated experimentally by high-speed photography and acoustic measurements. The elastic material consists of a polyacrylamide (PAA) gel whose elastic properties can be controlled by modifying the water content of the sample. The elastic modulus, E, is varied between 0.017 MPa and 2.03 MPa, and the dimensionless bubble boundary distance, [gamma], is for each value of E varied between [gamma] = 0 and [gamma] = 2.2. In this parameter space, jetting behaviour, jet velocity, bubble migration and bubble oscillation time are determined. The jetting behaviour varies between liquid jet formation towards or away from the elastic boundary, and formation of an annular jet which results in bubble splitting and the subsequent formation of two very fast axial liquid jets flowing in opposite directions. The liquid jet directed away from the boundary reaches a maximum velocity between 300 ms[minus sign]1 and 600 ms[minus sign]1 (depending on the elastic modulus of the sample) while the peak velocity of the jet directed towards the boundary ranges between 400 ms[minus sign]1 and 800 ms[minus sign]1 (velocity values averaged over 1 [mu]s). Penetration of the elastic boundary by the liquid jet is observed for PAA samples with an intermediate elastic modulus between 0.12 and 0.4 MPa. In this same range of elastic moduli and for small [gamma]-values, PAA material is ejected into the surrounding liquid due to the elastic rebound of the sample surface that was deformed during bubble expansion and forms a PAA jet upon rebound. For stiffer boundaries, the bubble behaviour is mainly characterized by the formation of an axial liquid jet and bubble migration directed towards the boundary, as if the bubble were adjacent to a rigid wall. For softer samples, the bubble behaviour becomes similar to that in a liquid with infinite extent. During bubble collapse, however, material is torn off the PAA sample when bubbles are produced close to the boundary. We conclude that liquid jet penetration into the boundary, jet-like ejection of boundary material, and tensile-stress-induced deformations of the boundary during bubble collapse are the major mechanisms responsible for cavitation erosion and for cavitation-enhanced ablation of elastic materials as, for example, biological tissues.

Brujan, Emil-Alexandru; Nahen, Kester; Schmidt, Peter; Vogel, Alfred

2001-04-01

82

Laser-Induced Dynamical Chirality and Intramolecular Energy Flow in the CH Chromophore  

SciTech Connect

We review the quantum dynamics of intramolecular energy flow during and after coherent infrared multiphoton excitation of the CH organic chromophore. The understanding of the underlying dynamics is of central importance for a wide range of systems in molecular physics, chemistry and biology, due to the experimentally supported assumption that the chromophore dynamics is weakly-dependent on a specific environment, in particular on sub-picosecond time scale. The excitation process due to the interaction with the laser field is studied by computationally monitoring the wave packet motion in the configuration sub-space relevant to femtosecond dynamics, using global analytical potential energy and electric dipole functions previously developed. The features of the intramolecular vibrational energy redistribution and the related dynamical time scales are investigated. In particular, we discuss the generation of dynamical chirality in methane istopomers, the corresponding stereomutation and racemization phenomena on the femtosecond time scale, and their relation to intramolecular vibrational energy redistribution.

Thanopulos, Ioannis [Department of Chemistry, University of British Columbia, Vancouver, B.C. V6T 1Z3 (Canada)

2007-11-29

83

Dynamic and static strain gauge using superimposed fiber Bragg gratings  

NASA Astrophysics Data System (ADS)

This paper demonstrates a simple and fast interrogation method for the dynamic and/or static strain gauge using a reflection spectrum from two superimposed fiber Bragg gratings (FBGs). The superimposed FBGs are designed to decrease nonequidistant space of generated a sensing pulse train in a time domain during dynamic strain gauge. By combining centroid finding with smooth filtering methods, both the interrogation speed and accuracy are improved. A four times increase in the interrogation speed of dynamic strain, by generating a 2 kHz optical sensing pulse train from a 500 Hz scanning frequency, is demonstrated experimentally. The interrogation uncertainty and total harmonic distortion characterization of superimposed FBGs are tested and less than 4 pm standard deviation is obtained.

Ma, Y. C.; Yang, Y. H.; Li, J. M.; Yang, M. W.; Tang, J.; Liang, T.

2012-10-01

84

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

National Technical Information Service (NTIS)

Photogrammetry has proven to be a valuable tool for static and dynamic profiling of membrane based inflatable and ultra-lightweight space structures. However, the traditional photogrammetric targeting techniques used for solid structures, such as attached...

A. A. Dorrington T. W. Jones P. M. Danehy R. S. Pappa

2003-01-01

85

X-ray reflection by rough multilayer gratings: Dynamical and kinematical scattering  

Microsoft Academic Search

X-ray reflectivity by rough multilayer gratings is treated in the framework of kinematical and dynamical theories. The kinematical scattering integral is calculated without the restrictions of the Fraunhofer approximation. The dynamical theory is presented by the matrix modal eigenvalue approach. In both theories we generalize the Fresnel reflection and transmission coefficients for the case of grating diffraction. We obtain one

P. Mikulík; T. Baumbach

1999-01-01

86

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

SciTech Connect

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

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

2010-09-03

87

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

88

Laser-induced decomposition and ablation dynamics studied by nanosecond interferometry  

Microsoft Academic Search

A polyurethane sample film was prepared by adding phenol resin as a structural stabilizer and its laser ablation dynamics was studied upon excimer laser irradiation. The ablation threshold by 248nm excitation was determined to be 40mJ\\/cm2 and no appreciable debris was left. The etch depth increases with the fluence and reaches 0.5?m at the fluence of 1J\\/cm2. Time-resolved interferometric images

Tomokazu Masubuchi; Hiroshi Fukumura; Hiroshi Masuhara; Kenkichi Suzuki; Nobuaki Hayashi

2001-01-01

89

Under-the-Barrier Dynamics in Laser-Induced Relativistic Tunneling  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

90

Fiber Bragg grating sensors for dynamic machining applications  

NASA Astrophysics Data System (ADS)

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

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

2003-11-01

91

Tunable and reconfigurable multi-tap microwave photonic filter based on dynamic Brillouin gratings in fibers.  

PubMed

We propose and experimentally demonstrate new architectures to realize multi-tap microwave photonic filters, based on the generation of a single or multiple dynamic Brillouin gratings in polarization maintaining fibers. The spectral range and selectivity of the proposed periodic filters is extensively tunable, simply by reconfiguring the positions and the number of dynamic gratings along the fiber respectively. In this paper, we present a complete analysis of three different configurations comprising a microwave photonic filter implementation: a simple notch-type Mach-Zehnder approach with a single movable dynamic grating, a multi-tap performance based on multiple dynamic gratings and finally a stationary grating configuration based on the phase modulation of two counter-propagating optical waves by a common pseudo-random bit sequence (PRBS). PMID:22418495

Sancho, J; Primerov, N; Chin, S; Antman, Y; Zadok, A; Sales, S; Thévenaz, L

2012-03-12

92

Local Investigation of Femtosecond Laser Induced Dynamics of Water Nanoclusters on Cu(111)  

NASA Astrophysics Data System (ADS)

We explore the dynamics of low temperature interfacial water nanoclusters on Cu(111) by femtosecond-laser excitation, scanning tunneling microscopy and density functional theory. Laser illumination is used to induce single molecules to diffuse within water clusters and across the surface, breaking and reforming hydrogen bonds. A linear diffusion probability with laser fluence is observed up to 0.6J/m2 and we suggest that diffusion is initiated by hot electron attachment and detachment processes. The density functional calculations shed light on the detailed molecular mechanism for water diffusion that is determined by the local structure of the water clusters.

Mehlhorn, Michael; Carrasco, Javier; Michaelides, Angelos; Morgenstern, Karina

2009-07-01

93

Optical control of laser induced chaotic dynamics in nematic liquid crystals  

NASA Astrophysics Data System (ADS)

The torque exerted by light on a liquid crystal is known to induce molecular reorientation and an ordinary linearly polarized light with small oblique incidence may generate a transition to chaos via a cascade of gluing bifurcations. In this work, we discuss the possibility to control such a chaotic dynamics either by judicious small perturbations of the intensity of the excitation light or by using a self-controlled feedback. These control procedures are investigated in the context of a real system, where only partial information on the chaotic attractor can be retrieved. Properties of the two approaches (transient time to control, robustness against noise ...) are studied and compared for their individual merits with the perspective of an efficient experimental implementation.

Brasselet, E.; Doyon, B.; Dubé, L. J.

2004-03-01

94

Dynamics Of A Laser-Induced Plume Self-Similar Expansion  

SciTech Connect

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

Bennaceur-Doumaz, D. [Advanced Technologies Development Centre, B. P. 17 Baba Hassen 16303, Algiers (Algeria); Djebli, M. [Advanced Technologies Development Centre, B. P. 17 Baba Hassen 16303, Algiers (Algeria); Theoretical Phys. Lab., Faculty of Physics-USTHB-B. P. 32 Bab Ezzouar 16079, Algiers (Algeria)

2008-09-23

95

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

PubMed

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

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

2010-11-10

96

Dynamics of macaque MT cell responses to grating triplets  

PubMed Central

Neurons in area MT are sensitive to the direction of motion of gratings and of plaids made by summing 2 gratings moving in different directions. MT component-direction-selective (CDS) neurons respond to the individual gratings of a plaid. Pattern-direction-selective (PDS) neurons on the other hand, combine component information and respond selectively to the resulting pattern motion. Adding a third grating creates a “triplaid“, which contains 3 grating and 3 plaid motions and is perceptually multistable. To examine how direction selective mechanisms parse the motion signals in triplaids, we recorded MT responses of anesthetized and awake macaques to stimuli in which 3 identical moving gratings whose directions were separated by 120 deg were introduced in 3 successive epochs, going from grating to plaid to triplaid. CDS and PDS neurons – selected based on their responses to gratings and plaids – had strikingly different tuning properties in the triplaid epoch. CDS neurons were strongly tuned for the direction of motion of individual gratings, but PDS neurons nearly lost their selectivity for either the gratings or the plaids in the stimulus. We can explain this reduced motion selectivity with a model that relates pattern selectivity of PDS neurons to a broad pooling of V1 afferents with a near-cosine weighting profile. Because PDS neurons signal both component and pattern motion in gratings and plaids, their reduced selectivity for motion in triplaids may be what makes these stimuli perceptually multistable.

Jazayeri, Mehrdad; Wallisch, Pascal; Movshon, J. Anthony

2012-01-01

97

Time-dependent dynamics of intense laser-induced above threshold Coulomb explosion  

NASA Astrophysics Data System (ADS)

We use our recently proposed model [1] to extract information about the nuclear dynamics from the recent Coulomb explosion data of Staudte et al. taken with 40 fs pulses [2]. That data, taken at multiple intensities near the ionization appearance intensity for both H2 and D2 in linearly and circularly polarized light, shows remarkable structure and regularity not easily explained by conventional models. Because our model does fit the spectra well, we can infer the qualitative time-dependent evolution of the system. In addition, we speculate about the possibility of rescattering leading to above threshold Coulomb explosion. [1] B.D. Esry, A.M. Sayler, P.Q. Wang, K.D. Carnes, and I. Ben-Itzhak, Phys. Rev. Lett. 97, 013003 (2006). [2] A. Staudte, D. Pavici'c, S. Chelkowski, D. Zeidler, M. Meckel, H. Niikura, M. Sch"offler, S. Sch"ossler, B. Ulrich, P. P. Rajeev, Th. Weber, T. Jahnke, D.M. Villeneuve, A.D. Bandrauk, C.L. Cocke, P.B. Corkum, and R. D"orner, Phys. Rev. Lett. (accepted).

Esry, B. D.; Ben-Itzhak, I.

2007-06-01

98

Photo-excitation dynamics of malachite green in ionic liquids studied by the transient grating method  

NASA Astrophysics Data System (ADS)

Photo-excitation dynamics of malachite green in ionic liquids has been studied by the transient grating method. Anomalies of the S1 lifetime and vibrational energy relaxation are found together with the structural relaxation of ionic liquid.

Fukuda, Masanori; Kajimoto, Okitsugu; Terazima, Masahide; Kimura, Yoshifumi

99

Research on dynamic error correction method for NC rotary table based on time grating sensor  

NASA Astrophysics Data System (ADS)

In order to apply original absolute time grating sensor to closed loop numerical control system, a forecasting angle displacement method with time series analysis theory is proposed. In this way, an absolute time grating sensor can be transformed to an incremental time grating. In addition, a discrete standard quantity interpolation method is present to reduce dynamic forecast error. In this way, forecast error of the last measurement period will be corrected in the next measurement period. Therefore, cumulative errors can be eliminated. The experiment results prove that dynamic errors can be controlled within +/-3" with error correction method.

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

2011-08-01

100

Lens-free heterodyne transient grating method for dynamics measurement of photoexcited species in liquid  

NASA Astrophysics Data System (ADS)

A recently developed lens-free heterodyne transient grating method was applied for the measurement of ultrafast photoexcited dynamics of several kinds of dye molecules in aqueous solutions. The principle of the lens-free heterodyne transient grating method was clarified in detail, especially for thick samples, such as liquid and semi-transparent solid samples. The ultrafast dynamics of malachite green and methyl orange molecules in aqueous solutions was successfully monitored, and the obtained time constants agreed with those in other reports.

Yamaguchi, M.; Katayama, K.; Sawada, T.

2003-08-01

101

Laser Induced Photochemistry.  

National Technical Information Service (NTIS)

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

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

1979-01-01

102

Dynamics of plasma gratings in atomic and molecular gases  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

103

All-optical dynamic grating generation based on Brillouin scattering in polarization-maintaining fiber.  

PubMed

We report a novel kind of all-optical dynamic grating based on Brillouin scattering in a polarization maintaining fiber (PMF). A moving acoustic grating is generated by stimulated Brillouin scattering between writing beams in one polarization and used to reflect an orthogonally polarized reading beam at different wavelengths. The center wavelength of the grating is controllable by detuning the writing beams, and the 3 dB bandwidth of approximately 80 MHz is observed with the tunable reflectance of up to 4% in a 30 m PMF. PMID:18451941

Song, Kwang Yong; Zou, Weiwen; He, Zuyuan; Hotate, Kazuo

2008-05-01

104

Operation of Brillouin dynamic grating in single-mode optical fibers.  

PubMed

The first (to our knowledge) observation of Brillouin dynamic grating in conventional single-mode fibers is reported, and the characterization is demonstrated with respect to the external parameters for the grating generation. When a 100 m single-mode fiber is used, a reflectance of 8% with a spectral bandwidth as low as 2.4 MHz is achieved, which is less than 10% of ordinary Brillouin gain bandwidth. PMID:22139284

Song, Kwang Yong

2011-12-01

105

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

Microsoft Academic Search

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

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

2011-01-01

106

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

107

Dynamic space shaping of intense ultrashort laser light with blazed-type gratings.  

PubMed

A beam shaper for dynamic transversal shaping of broadband laser pulses that utilizes a blazed ruled grating and a blazed-type grating simulated on Spatial Light Modulator was demonstrated. The introduced shaper scheme is an extension of 2f-2f scheme [Mariyenko, et al., Opt. Express 13, 7599 (2005)] where the two thin holograms with matched grating constants performed light shaping. The new scheme utilizes the diffraction gratings with different grating constants. Dispersion-free light shaping is achieved by means of the intermediate transversal light beam magnification. The magnification balances the mismatch in the grating constants resulting in total residual angular dispersion compensation. In turn, the magnified beam covers a greater area on the modulator matrix thus reducing the incident light power density by a value equal to square of the magnification factor. It translates to the safe-operation threshold extension of the modulator allowing shaping pulses that are powerful enough to be used in the applications. With a proper components selection, the throughput efficiency of the shaper can be well above 40%. A proper shaper operation was demonstrated with the 140-fs Ti:Sapphire oscillator. Theoretical calculations support the conclusions. PMID:21164860

Marienko, I; Denisenko, V; Slusar, V; Soskin, M

2010-11-22

108

Dynamic analysis and temperature measurements of concrete cantilever beam using fibre Bragg gratings  

Microsoft Academic Search

We analyzed the action of fire, causing degradation in a concrete cantilever beam using dynamic testing. The structure was fitted with two fibre Bragg gratings (FBG) sensors. One of them measured vibration and the other measured the temperature inside of the cantilever beam, while the beam was exposed to fire. A high-temperature probe based on a simple packaging system, which

Jean Carlos Cardozo da Silva; Cicero Martelli; Hypolito José Kalinowski; Elisabeth Penner; John Canning; Nathaniel Groothoff

2007-01-01

109

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

110

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

111

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

Microsoft Academic Search

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

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

2007-01-01

112

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

Microsoft Academic Search

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

L. K. Cheng; W. C. Prinse

113

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

NASA Astrophysics Data System (ADS)

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

Thurlby, J. A.

1988-02-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

115

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

116

Structure and property changes and femtosecond laser-induced magnetization dynamics of two-year-old high coercive TbFeCo films  

NASA Astrophysics Data System (ADS)

An uncoated TbFeCo film on glass substrate exposed to dry air for 2 years is studied using magneto-optical polar Kerr spectroscopy and vibrating sample magnetometry (VSM). The out-of-plane hysteresis loop by VSM is found to become slanted and meanwhile, an in-plane loop is also observable. The Kerr loop measured from the exposed surface is also slanted compared to that measured from the substrate-contacted surface, which indicates that the exposed surface is oxidized. So a bilayer structure of the film is proposed. When a pump laser is switched on, the Kerr loops measured from both surfaces at the delay time of -5 ps become anomalous, showing the occurrence of magnetization reversal across magnetization compensation temperature. Unlike that measured from the substrate-contacted surface, femtosecond laser-induced magnetization dynamics measured from the exposed surface does not show magnetization reversal crossing zero magnetization. This can be explained by the bilayer structure as the compensation effect of demagnetization recovery of the oxidized layer on magnetization reversal of perpendicularly anisotropic TbFeCo layer across magnetization compensation temperature. Above experimental results show that the uncoated TbFeCo film cannot resist oxidation in dry air at room temperature for 2 years while the SiO2-coated surface can do so for over 2 years.

Xu, Chudong; Chen, Zhifeng; Yang, Xu; Li, Shufa; Chen, Daxin; Zhou, Shiming; Lai, Tianshu

2012-07-01

117

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

118

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

PubMed

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

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

2012-03-01

119

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

120

High-Density Integrated-Optical Switch Arrays Based on Dynamic Waveguide Gratings  

NASA Astrophysics Data System (ADS)

Integrated-optical switch arrays have many potential uses ranging from long haul communications to computer based optical interconnects. A key factor that has limited the practical application of previous switch designs is their relatively low densities. While many applications require switch networks of at least 100 x 100 elements, the state-of-the-art in monolithic optical switch arrays is only 16 x 16 elements implemented in LiNbO_3 . We have demonstrated a new type of integrated -optical switch element, based on dynamic waveguide gratings, which we believe will allow monolithic integration of arrays of more than 100 x 100 elements. These devices have been implemented in two very different material systems, LiNbO _3 and GaAs. The LiNbO_3 devices are based on photorefractive gratings which are written optically. These devices are able to achieve high density but have slow switching speeds. The GaAs based devices make use of free carrier gratings. Free carrier effects can provide large refractive index changes which may be electrically controlled at very high speeds. Several implementations of the dynamic free carrier grating switch are described, including theoretical predictions of the diffraction efficiency of the various designs. The fabrication process and optical testing of a low efficiency proof-of-principle design based on Schottky depletion of an implanted free carrier grating is discussed. Experimental diffraction efficiency measurements are presented and a detailed theoretical analysis of the diffraction efficiency vs. wavelength data is given. Finally, recommendations are made for future research and the outlook for a practical monolithic 100 x 100 element switch array is examined and is found to be quite promising.

Aronson, Lewis Bernard

1992-01-01

121

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

PubMed

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

Klinkusch, Stefan; Saalfrank, Peter; Klamroth, Tillmann

2009-09-21

122

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

123

Laser-induced clustering dynamics of [(SiO 2) nX] - from porous silica powders  

NASA Astrophysics Data System (ADS)

The clustering dynamics of SiO 2-containing negative ion clusters generated from ultrafine amorphous SiO 2 powders with high specific surface area is investigated by XeCl excimer laser ablation time-of-flight mass spectrometry (TOF-MS). From the evolution of the mass spectra with the delay time and the number of laser irradiation shots, the key roles played by OH and OH - fragments from the surface silanol groups in the formation of SiO 2-containing negative ion clusters are discussed.

Xu, Can; Wang, Liwei; Qian, Shixiong; Zhao, Li; Wang, Zichen; Li, Yufen

1997-12-01

124

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

PubMed

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 and pH value of running buffer, separation voltage and detection site. Through comparing electroosmotic flow, plate numbers and other parameters, an acceptable separation condition was obtained. Under optimized conditions, the precisions of RB detection (R.S.D., n=10) were 2.62% for migration time, 4.78% for peak height respectively. Additionally, RB concentration linearity response was excellent with 0.9996 of correlation coefficient between 1 and 100muM, and a limit of detection (S/N=3) was 0.2muM. Finally, we separated rhodamine B isothiocyanate and lysine deriving from the fluorescent probe, and the result displayed that the dynamic coating method was applicable by CE separations using PDMS/glass chip. PMID:18970086

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

2005-05-15

125

Observation of the laser-induced surface dynamics by the single-shot x-ray laser interferometer  

NASA Astrophysics Data System (ADS)

We have developed a soft x-ray laser (SXRL) interferometer capable of the single-shot imaging of nano-scaled structure dynamics. The interferometer consisted of the reflection optics including double Lloyd's mirrors and focusing optics, and the interference fringes are produced on the detector surface. The depth and lateral resolutions of the interferometer were about 1 nm and 1.8 ?m, respectively. By using this interferometer, the initial stage (~50 ps) of the ablation process of the Pt surface pumped by a 70 fs Ti:Sapphire laser pulse was observed. The expansion speed of the surface estimated from the result (34 nm/50 ps) indicated that the nano-bubble structures were formed in the initial stage of the ablation. In order to observe the detailed dynamics, the temporal synchronization between the pump and probe pulses was improved to be 3 ps by adopting a portion of the SXRL and pump beams as the time fiducials, to which the pump and probe timing was adjusted by using the x-ray streak camera.

Hasegawa, Noboru; Ochi, Yoshihiro; Kawachi, Tetsuya; Nishikino, Masaharu; Ishino, Masahiko; Imazono, Takashi; Kaihori, Takeshi; Sasaki, Akira; Terakawa, Kota; Minami, Yasuo; Tomita, Takuro; Yamamoto, Minoru; Umeda, Yoshifumi; Yamagiwa, Mitsuru; Suemoto, Tohru

2011-09-01

126

Ultrafast laser-induced magnetization precession dynamics in FePt/CoFe exchange-coupled films  

NASA Astrophysics Data System (ADS)

Femtosecond laser-triggered magnetization precession dynamics in exchange-coupled hard FePt/soft CoFe films has been studied by the time-resolved magneto-optical Kerr effect. The precession frequency is shown to be independent of the CoFe thickness tCoFe, while linearly proportional to the external field for the sample with tCoFe=7 nm, implying that the magnetization relaxation is governed by a uniform precession mode. The result agrees well with the theoretical prediction based on the Landau-Lifshitz-Gilbert equation. The obtained damping factor ?~0.13 is quite large and is thought to be dominated by the FePt layer. Additionally, the oscillation amplitude strongly depends on the CoFe thickness with a maximum value occurred at tCoFe=7 nm.

Zhang, Zongzhi; Cui, Boyin; Wang, Guangzhong; Ma, B.; Jin, Q. Y.; Liu, Yaowen

2010-10-01

127

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

SciTech Connect

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

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

2011-04-15

128

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

129

Tunable quasi-phase matching using dynamic ferroelectric domain gratings induced by photorefractive space-charge fields  

Microsoft Academic Search

We demonstrate a method of dynamic, tunable quasi-phase matched second-harmonic generation using optically induced polarization gratings with periods equal to twice the coherence length. These gratings increase the peak second-harmonic conversion efficiency by a factor of 17 above a poled strontium barium niobate crystal, to 0.01% for fundamental beam intensities of 0.8 MW cm?2. We generate quasi-phase matching spectral response

Anthony S. Kewitsch; Mordechai Segev; Amnon Yariv; Gregory J. Salamo; Terrence W. Towe; Edward J. Sharp; Ratnakar R. Neurgaonkar

1994-01-01

130

Temporal and spatial dynamics of laser-induced aluminum plasma in argon background at atmospheric pressure: Interplay with the ambient gas  

Microsoft Academic Search

Laser ablation in background gas implies supplementary complexities with respect to what happens in the vacuum. It is however essential to understand in detail the involved mechanisms for a number of applications requiring the ablation to be performed in an ambient gas at relative high pressure, such as pulsed-laser deposition, or laser-induced breakdown spectroscopy. In this paper, the expansion of

Q. L. Ma; V. Motto-Ros; W. Q. Lei; M. Boueri; X. S. Bai; L. J. Zheng; H. P. Zeng; J. Yu

131

Estimation of dynamic structural displacements using fiber Bragg grating strain sensors  

NASA Astrophysics Data System (ADS)

This study investigates dynamic structural displacements estimation using displacement strain relationship and measured strain data. Strain signals are obtained from fiber Bragg grating (FBG) sensors that have an excellent multiplexing ability. Vibration experiments were performed with aluminum and acryl beam specimens. The beam structures were subjected to various loading conditions, and deformed shapes were reconstructed by using strain signals. The estimated displacements show good agreements with those measured directly from laser displacement sensors. In present study, it is confirmed structural displacements can be estimated using strain data without displacement measurement.

Kang, Lae-Hyong; Kim, Dae-Kwan; Han, Jae-Hung

2007-08-01

132

Laser induced ignition  

NASA Astrophysics Data System (ADS)

Nowadays, combustion engines and other combustion processes play an overwhelming and important role in everyday life. As a result, ignition of combustion processes is of great importance, too. Usually, ignition of a combustible material is defined in such a way that an ignition initiates a self-sustained reaction which propagates through the inflammable material even in the case that the ignition source has been removed. In most cases, a well defined ignition location and ignition time is of crucial importance. Spark plugs are well suited for such tasks but suffer from some disadvantages, like erosion of electrodes or restricted positioning possibilities. In some cases, ignition of combustible materials by means of high power laser pulses could be beneficial. High power lasers offer several different possibilities to ignite combustible materials, like thermal ignition, resonant ignition or optical breakdown ignition. Since thermal and resonant ignitions are not well suited on the requirements mentioned previously, only optical breakdown ignition will be discussed further. Optical breakdown of a gas within the focal spot of a high power laser allows a very distinct localization of the ignition spot in a combustible material. Since pulse duration is usually in the range of several nanoseconds, requirements on the ignition time are fulfilled easily, too. Laser peak intensities required for such an optical breakdown are in the range of 1011 W/cm2. The hot plasma which forms during this breakdown initiates the following self-propagating combustion process. It has been shown previously that laser ignition of direct injection engines improves the fuel consumption as well as the exhaust emissions of such engines significantly. The work presented here gives a brief overview on the basics of laser induced ignition. Flame propagation which follows a successful ignition event can be distinguished into two diffrent regimes. Combustion processes within an engine are usually quite slow - the reaction velocity is mainly determined by the heat conductivity of the combustible. Such deflagrations processes show propagation velocities well below the speed of sound. On the other hand, detonations show much higher propagation velocities. In contrast to deflagrations, detonations show propagation velocities higher than the speed of sound within the combustible. The shock front which propagates through a combustible in the case of a detonation is responsible for a considerable pressure gradient moving at supersonic velocity. Basics and possible examples of laser induced ignitions of deflagrations and detonations are given and pros and cons of laser ignition systems are discussed briefly.

Liedl, G.; Schuöcker, D.; Geringer, B.; Graf, J.; Klawatsch, D.; Lenz, H. P.; Piock, W. F.; Jetzinger, M.; Kapus, P.

2007-05-01

133

Laser-Induced Plasma In a Water Bubble  

SciTech Connect

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

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

2005-05-16

134

The photodissociation and reaction dynamics of vibrationally excited molecules  

SciTech Connect

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

Not Available

1993-01-01

135

Accuracy and uncertainty of single-shot, nonresonant laser-induced thermal acoustics  

Microsoft Academic Search

We study the accuracy and uncertainty of single-shot nonresonant laser-induced thermal acoustics measurements of the speed of sound and the thermal diffusivity in unseeded atmospheric air from electrostrictive gratings as a function of the laser power settings. For low pump energies, the measured speed of sound is too low, which is due to the influence of noise on the numerical

Stefan Schlamp; Hans G. Hornung; Thomas H. Sobota; Eric B. Cummings

2000-01-01

136

Laser-induced plasmas from the ablation of metallic targets: The problem of the onset temperature, and insights on the expansion dynamics  

SciTech Connect

Laser-induced plasmas are transient systems rapidly aging in few nanoseconds of evolution. Time-of-flight spectrometry allowed studying initial plasma characteristics based on frozen translational degrees of freedom, hence overcoming intrinsic limitations of optical spectroscopy. Experimental ion velocity distributions were reconstructed as developed during the longitudinal plasma expansion. The obtained onset plasma temperatures are in the range of {approx}18-45 eV depending on the ablated metals. Also the ion angular spreads were found to be a function of ablated metal, e.g., the narrowest for Fe, the broadest for Al, due to different collisional coupling in the plasma population.

Bleiner, Davide; Bogaerts, Annemie; Belloni, Fabio; Nassisi, Vincenzo [Department of Chemistry, University of Antwerpen, Universiteitsplein 1, Antwerp, 2610 Flanders (Belgium); Department of Physics, University of Lecce, via Arnesano, CP 193, 73100 Lecce (Italy)

2007-04-15

137

Electrically controlled dynamic holographic gratings in fullerene C60-doped nematic liquid crystals  

NASA Astrophysics Data System (ADS)

A new method to demonstrate the dynamic enhancement of the photorefractive effect in C60-doped homeotropically aligned 4-cyano-4'-pentyl-biphenyl (5CB) liquid crystals under the influence of an externally applied dc voltage is presented in the read-out process. We observed clear holographic images due to the transient diffraction efficiency enhancement controlled by the application of a dc voltage. The hidden gratings are due to a light-induced surface-charge modulation and amplified by the Carr-Helfrich effect in the presence of the electric field produced by the dc voltage. A qualitative analysis of the phenomenon, according to which the effective bulk voltage is modulated due to light-induced surface modifications, is proposed. We achieved the highest transient first-order diffraction efficiency of up to 40%. The effective nonlinear index coefficient is as large as 0.2 cm2 W-1.

Sun, Xiudong; Ren, Changyu; Pei, Yanbo; Yao, Fengfeng

2008-12-01

138

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

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

139

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

140

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

2012-03-01

141

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

SciTech Connect

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

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

1993-02-01

142

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

SciTech Connect

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

Not Available

1993-04-01

143

Laser pulse induced gold nanoparticle gratings  

Microsoft Academic Search

We report the results of our experimental investigation of laser induced gold nanoparticle gratings and their optical diffraction properties. A single shot of a pair Nd-YAG laser pulses with the same polarization is directed toward a 6 nm thick gold film on a substrate of polymethyl methacrylate. As a result of the laser illumination, the thin gold film is fragmented

Wen-Chi Hung; Wood-Hi Cheng; Ming-Shan Tsai; Wei-Chih Chung; I.-Min Jiang; Pochi Yeh

2008-01-01

144

A Model of Laser-Induced Cavitation  

NASA Astrophysics Data System (ADS)

Evaporation and plasma formation due to laser irradiation and subsequent expansion of the evaporated volume accompanying shock emission were studied theoretically as a phenomenon of laser-induced thermal breakdown rather than an optic breakdown. In recent years, this problem has become particularly important in the field of laser-mediated surgery. The Gilmore model of bubble dynamics based on the Kirkwood-Bethe hypothesis with proper initial conditions was used to calculate the shock pressure. This pressure depends on the radius and expansion velocity of the plasma formed by the laser irradiation. Subsequent bubble evolution after shock departure including the light emission at the collapse point was studied using the Keller-Miksis equation for the bubble wall motion and analytical solutions for the vapor inside the bubble. Calculation results show that the maximum size of the bubble and the half-width of the emitted power of the light pulse at the collapse point depend on the initial bubble radius and the bubble wall velocity. The light emission from the laser-induced bubble at the collapse point turns out to be black body radiation.

Byun, Ki-Taek; Kwak, Ho-Young

2004-02-01

145

Reaction dynamics of Si(3PJ)+O2-->SiO(X 1?+)+O studied by a crossed-beam laser-induced fluorescence technique  

NASA Astrophysics Data System (ADS)

Oxidation reaction of the ground state Si atom was studied by using a crossed molecular beam technique at 13.0 kJ/mol of collision energy. The Si atomic beam was generated by laser vaporization and crossed with the oxygen molecular beam at right angle. Products at the crossing region were detected by the laser-induced fluorescence (LIF). The LIF of SiO(A 1?-X 1?+) was used to determine the vibrational state distribution of the electronic ground state, SiO(X 1?+). The determined distribution was inverted with the maximum population at v''=4, and in good agreement with the recent quasiclassical trajectory calculation on the singlet potential energy surface. The agreement suggested that an abstraction mechanism is dominant at the collision energy studied here. One of the counterproducts, O(3PJ), was also observed by the vacuum ultraviolet LIF and the distribution of the spin-orbit levels were determined. The formation of O(3PJ) was consistent with the significant population of v''=7 and 8 states of SiO, which could be explained by the presence of the triplet product channel with higher exothermicity.

Yamashiro, R.; Matsumoto, Y.; Honma, K.

2008-02-01

146

UV Bragg grating inscription in germanium-doped photonic crystal fibers  

NASA Astrophysics Data System (ADS)

The design flexibility of photonic crystal fibers has accelerated the development of specialty optical fibers for a wide variety of applications. Optical fiber sensor applications for instance can benefit from this fiber technology. Fiber Bragg grating inscriptions in photonic crystal fibers have been reported with inscription setups that go from continuous-wave to femtosecond pulsed laser sources. However, the compatibility of the microstructures in these fibers with conventional ultraviolet inscription techniques was never before investigated in a broad range of (Germanium doped) fibers. We present UV laser induced dynamics of Bragg gratings growths in photonic crystal fibers with a hexagonal arrangement of 6 rings of airholes around a Germanium doped core region. The average refractive index increase and the refractive index modulation by the grating inscription process are compared for microstructures with several doping levels, airhole filling factors, airhole pitch distance and fiber orientation. We show how the parameters of the microstructure can influence the Bragg grating inscriptions. In addition we expand the range of fibers in which Bragg gratings, with reflection strengths that are useable for sensing purposes, can be inscribed to fibers with Germanium doping concentrations as low as 1.36 and 0.45 mol%.

Geernaert, Thomas; Becker, Martin; Mergo, Pawel; Nasilowski, Tomasz; Wojcik, Jan; Urbanczyk, Waclaw; Rothhardt, Manfred; Chojetzki, Christoph; Bartelt, Hartmut; Berghmans, Francis; Thienpont, Hugo

2010-04-01

147

Luminescence mechanism of acoustic and laser-induced cavitation  

NASA Astrophysics Data System (ADS)

A new approach is proposed for explaining the experimental data on sonoluminescence of acoustic and laser-induced cavitation bubbles. It is suggested that two different sonoluminescence mechanisms, namely, thermal and electric ones, are possible and that they manifest themselves depending on the bubble dynamics. An intense thermal luminescence occurs as a result of compression of an individual stationary spherical bubble; a weak electric luminescence accompanies the deformation and splitting of the bubble when thermal luminescence is suppressed (for example, in the case of multibubble sonoluminescence). It is shown that, when an individual bubble loses its spherical shape under the effect of different actions (change in the acoustic pressure, artificial deformation, translatory motion, etc.) or when a laser-induced bubble undergoes fragmentation, the sonoluminescence spectrum exhibits specific bands that are similar to the bands in the multibubble sonoluminescence spectrum. The appearance of these bands is attributed to the suppression of the thermal sonoluminescence mechanism and the manifestation of the electric mechanism. It is shown that the maximum temperature T max characterizing the compression of a laser-induced bubble is primarily determined by the temperature of the plasma at the instant of the laser-induced breakdown, whereas, for an acoustic bubble, T max is primarily determined by the acoustic and hydrostatic pressures and by the saturation vapor pressure of the liquid.

Margulis, M. A.; Margulis, I. M.

2006-05-01

148

Laser induced melting and crystallization of boron doped amorphous silicon  

SciTech Connect

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

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

1997-07-01

149

Laser induced shock waves in deformation processing  

Microsoft Academic Search

Processes based on laser induced shock waves in deformation processing are reviewed in this paper. One widely used process is laser shock processing (LSP) for mechanical surface hardening, which is presented on the basis of a literature inquiry. Two further processes are laser stretch forming and assistance of laser induced shock waves in bending of hybrid blanks. These two processes

H. Schulze Niehoff; F. Vollertsen

150

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

151

Nonspherical laser-induced cavitation bubbles.  

PubMed

The generation of arbitrarily shaped nonspherical laser-induced cavitation bubbles is demonstrated with a optical technique. The nonspherical bubbles are formed using laser intensity patterns shaped by a spatial light modulator using linear absorption inside a liquid gap with a thickness of 40 microm. In particular we demonstrate the dynamics of elliptic, toroidal, square, and V-shaped bubbles. The bubble dynamics is recorded with a high-speed camera at framing rates of up to 300,000 frames per second. The observed bubble evolution is compared to predictions from an axisymmetric boundary element simulation which provides good qualitative agreement. Interesting dynamic features that are observed in both the experiment and simulation include the inversion of the major and minor axis for elliptical bubbles, the rotation of the shape for square bubbles, and the formation of a unidirectional jet for V-shaped bubbles. Further we demonstrate that specific bubble shapes can either be formed directly through the intensity distribution of a single laser focus, or indirectly using secondary bubbles that either confine the central bubble or coalesce with the main bubble. The former approach provides the ability to generate in principle any complex bubble geometry. PMID:20365461

Lim, Kang Yuan; Quinto-Su, Pedro A; Klaseboer, Evert; Khoo, Boo Cheong; Venugopalan, Vasan; Ohl, Claus-Dieter

2010-01-14

152

Nonspherical laser-induced cavitation bubbles  

NASA Astrophysics Data System (ADS)

The generation of arbitrarily shaped nonspherical laser-induced cavitation bubbles is demonstrated with a optical technique. The nonspherical bubbles are formed using laser intensity patterns shaped by a spatial light modulator using linear absorption inside a liquid gap with a thickness of 40?m . In particular we demonstrate the dynamics of elliptic, toroidal, square, and V-shaped bubbles. The bubble dynamics is recorded with a high-speed camera at framing rates of up to 300000 frames per second. The observed bubble evolution is compared to predictions from an axisymmetric boundary element simulation which provides good qualitative agreement. Interesting dynamic features that are observed in both the experiment and simulation include the inversion of the major and minor axis for elliptical bubbles, the rotation of the shape for square bubbles, and the formation of a unidirectional jet for V-shaped bubbles. Further we demonstrate that specific bubble shapes can either be formed directly through the intensity distribution of a single laser focus, or indirectly using secondary bubbles that either confine the central bubble or coalesce with the main bubble. The former approach provides the ability to generate in principle any complex bubble geometry.

Lim, Kang Yuan; Quinto-Su, Pedro A.; Klaseboer, Evert; Khoo, Boo Cheong; Venugopalan, Vasan; Ohl, Claus-Dieter

2010-01-01

153

Laser induced ignition of propellants  

NASA Astrophysics Data System (ADS)

Central to the study of laser induced ignition of propellants is the provision of the igniting pulsed laser. Single pulses delivering in excess of 10 J energy were considered desirable. Because of the delay, the required laser which was to be obtained through BRL was not immediately available and some doubt has been expressed as to whether it would become available in the current financial year. Accordingly, an emergency plan based on attempting to revive a defunct 211A pulsed ruby laser was put into operation. This laser became non-operational some time ago, due to the leakage of cooling water through a small pin hole into the pumping flash lamp. Contrary to the manufacturers' specifications, replacement of the failed component did not cure the problem but caused the output to drop by 2 orders of magnitude to around 200mJ.

Carleton, F. B.; Weinberg, F. J.

1987-07-01

154

Dynamics of Energy Transport in Molecular Crystals: The Picosecond Transient-Grating Method  

Microsoft Academic Search

Energy transport in molecular solids is investigated using a picosecond transient-grating technique. A model is presented which directly relates the rate of energy transport to the experimental observable. The diffusion coefficient for singlet electronic excitation transport is reported for pentacene in p-terphenyl. Acoustically induced optical absorption effects are also observed.

J. R. Salcedo; A. E. Siegman; D. D. Dlott; M. D. Fayer

1978-01-01

155

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

156

Compatibility Studies by Laser Induced Fluorescence.  

National Technical Information Service (NTIS)

Laser induced fluorescence (LIF) is an ultrasensitive spectroscopic technique that can be used to detect molecular species at concentration levels below the parts-per-billion range. In addition to this high degree of sensitivity, the narrow linewidth of t...

L. R. Dosser

1985-01-01

157

Treatment of Laser Induced Retinal Injuries.  

National Technical Information Service (NTIS)

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

M. Belkin N. Naveh

1989-01-01

158

Kinematics of Cold Excitons in the Laser Induced Exciton Trap  

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

159

A novel method to measure dynamic strain using optical-path controlled Mach-Zehnder interferometer and fiber Bragg grating sensor  

Microsoft Academic Search

We introduce a Mach-Zehnder interferometer whose optical path difference is controlled by a tunable optical delay line. Using the interferometer as a demodulator for fiber Bragg grating sensors, intensity-based measurement of dynamic strain with a wide range of 0~1880 ?strain and 0~1 kHz is experimentally demonstrated

Sung Chul Kang; Sang Bae Lee; Sang Sam Choi; Byoungho Lee

1998-01-01

160

Full-spectrum interrogation of fiber Bragg grating sensors for dynamic measurements in composite laminates  

NASA Astrophysics Data System (ADS)

This paper presents a new means for collecting fiber Bragg grating (FBG) data during drop-tower measurements used to assess damage to composite structures. The high repetition-rate collection process reveals transient features that cannot be resolved in quasi-static measurements. The experiments made at a repetition rate of about 500 Hz show that the detected FBG spectrum broadens for a short period of time and relaxes quickly to a narrower static state. Furthermore, this relaxation time increases dramatically as the strike count increases. The information gained by such measurements will enhance the ability to characterize and distinguish failure modes and predict the remaining lifetime in composite laminate structures.

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

2009-11-01

161

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

162

Dynamics of laser-induced electroconvection pulses.  

PubMed

We first report that, for planar nematic 4-methoxy-benzilidene-4-butylaniline (MBBA), the electroconvection threshold voltage has a nonmonotonic temperature dependence, with a well-defined minimum, and a slope of about -0.12 V/degrees C near room temperature at 70 Hz. Motivated by this observation, we have designed an experiment in which a weak continuous-wave absorbed laser beam with a diameter comparable to the pattern wavelength generates a locally supercritical region, or pulse, in dye-doped MBBA. Working 10-20 % below the laser-free threshold voltage, we observe a steady-state pulse shaped as an ellipse with the semimajor axis oriented parallel to the nematic director, with a typical size of several wavelengths. The pulse is robust, persisting even when spatially extended rolls develop in the surrounding region, and displays rolls that counterpropagate along the director at frequencies of tenths of Hz, with the rolls on the left (right) side of the ellipse moving to the right (left). Systematic measurements of the sample-voltage dependence of the pulse amplitude, spatial extent, and frequency show a saturation or decrease when the control parameter (evaluated at the center of the pulse) approaches approximately 0.3. We propose that the model for these pulses should be based on the theory of control-parameter ramps, supplemented with new terms to account for the advection of heat away from the pulse when the surrounding state becomes linearly unstable. The advection creates a negative feedback between the pulse size and the efficiency of heat transport, which we argue is responsible for the attenuation of the pulse at larger control-parameter values. PMID:15244722

Giebink, N C; Johnson, E R; Saucedo, S R; Miles, E W; Vardanyan, K K; Spiegel, D R; Allen, C C

2004-06-04

163

Laser induced dynamics of interacting small particles  

Microsoft Academic Search

We study the translational motion of two interacting polarizable nanospheres in the presence of a laser field. Dependences of the resulting paths on geometry, viscosity of the medium, polarization, and wavelength of the incident field are discussed. It is found that in general clustering trajectories are more probable thus favoring agglomeration, and that viscosity and circular polarization of the applied

F. Claro; P. Robles; R. Rojas

2009-01-01

164

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

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

165

Luminescence from acoustic-driven laser-induced cavitation bubbles  

PubMed

The influence of a continuous sound field on the first oscillation cycle and on the cavitation luminescence of a transient laser-induced bubble is investigated experimentally. The variation of the collapse phase is predicted with a simple numerical model and compared with experiment. Bubble dynamics is mainly influenced by three parameters: the phase of bubble generation, the size of the bubble, and the amplitude of the sound field. The experimentally found enhancement and reduction of the luminescence is discussed and several suggestions are made for further boosting of the collapse strength. PMID:11046430

Ohl

2000-02-01

166

Luminescence from acoustic-driven laser-induced cavitation bubbles  

NASA Astrophysics Data System (ADS)

The influence of a continuous sound field on the first oscillation cycle and on the cavitation luminescence of a transient laser-induced bubble is investigated experimentally. The variation of the collapse phase is predicted with a simple numerical model and compared with experiment. Bubble dynamics is mainly influenced by three parameters: the phase of bubble generation, the size of the bubble, and the amplitude of the sound field. The experimentally found enhancement and reduction of the luminescence is discussed and several suggestions are made for further boosting of the collapse strength.

Ohl, Claus-Dieter

2000-02-01

167

Laser induced forward transfer of conducting polymers  

Microsoft Academic Search

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

M. Kandyla; S. Chatzandroulis; I. Zergioti

2010-01-01

168

Treatment of Laser-Induced Retinal Injuries.  

National Technical Information Service (NTIS)

This study investigated the effect of steroids know for their inflammatory effect on the laser-induced retinal injury. In an attempt to minimized this we studied prostaglandin E2 (PGE2), known for their mediatory-role in any inflammatory reaction, as well...

M. Belkin N. Naveh

1989-01-01

169

Spectroscopic Applications of Laser-Induced Plasmas  

Microsoft Academic Search

Recent spectroscopic applications of laser-induced plasmas are reviewed. Virtually all substances are susceptible to breakdown when illuminated by a sufficiently intense laser beam. In a plasma, matter breaks apart into atoms, ions, and electrons, producing a visible flash and an audible popping sound due to the acoustical shock wave generated by the sudden, high-velocity expansion of matter outward from the

Vahid Majidi; Martha R. Joseph

1992-01-01

170

Laser induced fluorescence spectroscopy for FTU.  

National Technical Information Service (NTIS)

Laser induced fluorescence spectroscopy (LIFS) is based on the absorption of a short pulse of tuned laser light by a group of atoms and the observation of the resulting fluorescence radiation from the excited state. Because the excitation is resonant it i...

T. P. Hughes

1995-01-01

171

Laser-induced electric breakdown in solids  

Microsoft Academic Search

A review is given of recent experimental results on laser-induced electric breakdown in transparent optical solid materials. A fundamental breakdown threshold exists characteristic for each material. The threshold is determined by the same physical process as dc breakdown, namely, avalanche ionization. The dependence of the threshold on laser pulse duration and frequency is consistent with this process. The implication of

NICOLAAS BLOEMBERGEN

1974-01-01

172

Laser induced chemical vapor deposition of carbon  

Microsoft Academic Search

Initial results on laser-induced chemical vapor deposition using the visible radiation of an Ar+ laser are presented. Due to the smaller wavelength of Ar+ laser radiation in comparison to the infrared radiation of a CO2 laser used in earlier experiments, much finer patterns could be produced. The influence of laser irradiance on the deposition rate and widths of patterns was

G. Leyendecker; D. Bäuerle; P. Geittner; H. Lydtin

1981-01-01

173

Treatment of Laser Induced Retinal Injuries.  

National Technical Information Service (NTIS)

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

M. Belkin N. Naveh

1987-01-01

174

Laser-induced fluorescence-cued, laser-induced breakdown spectroscopy biological-agent detection  

Microsoft Academic Search

Methods for accurately characterizing aerosols are required for detecting biological warfare agents. Currently, fluorescence-based biological agent sensors provide adequate detection sensitivity but suffer from high false-alarm rates. Combining single-particle fluorescence analysis with laser-induced breakdown spectroscopy (LIBS) provides additional discrimination and potentially reduces false-alarm rates. A transportable UV laser-induced fluorescence-cued LIBS test bed has been developed and used to evaluate the

John D. Hybl; Shane M. Tysk; Shaun R. Berry; Michael P. Jordan

2006-01-01

175

Enhancement of Laser-Induced Fluorescence by Intense Terahertz Pulses in Gases  

Microsoft Academic Search

The enhancement of laser-induced fluorescence by in- tense terahertz pulses was studied both theoretically and experi- mentally using selected gases. Semiclassical physical picture incor- porating photoionization, electron heating, impact excitation, and dissociative recombination was used to explain the plasma dynam- ics under terahertz radiation in picosecond scale. The dependences of enhanced fluorescence on the terahertz field, laser intensity, and atomic

Jingle Liu; Xi-Cheng Zhang

2011-01-01

176

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

Microsoft Academic Search

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

Jianyong Wu; Joseph Sneddon

2004-01-01

177

Ground state C 2 density measurement in carbon plume using laser-induced fluorescence spectroscopy  

Microsoft Academic Search

The temporal evolution and spatial distribution of C2 molecules produced by laser ablation of a graphite target is studied using optical emission spectroscopy, dynamic imaging and laser-induced fluorescence (LIF) investigations. We observe peculiar bifurcation of carbon plume into two parts; stationary component close to the target surface and a component moving away from the target surface which splits further in

Dheerendra Yadav; Varun Gupta; Raj K. Thareja

2009-01-01

178

Photorefractive properties of a thiapyrylium-dye-sensitized polymer composite: the dynamics of holographic grating formation and erasure  

NASA Astrophysics Data System (ADS)

We present the photorefractive properties of a new organic composite operating at near IR wavelengths. The composite contains an ionic thiapyrylium dye, 4-(4-dimethylaminophenyl)- 2,6-diphenyl thiapyrylium perchlorate as a photocharge generation sensitizer, 4-(N,N- diethylamino)-((beta) )-nitrostyrene as a second order nonlinear optical chromophore, and poly(9-vinylcarbazole) as a host polymer which also serves as a charge transporting agent. Both degenerate and nondegenerate four-wave mixing experiments have been carried out and holographic diffraction efficiencies as high as 2% have been achieved. Asymmetric energy transfer has been observed with a gain of 7 cm-1 in a two-beam coupling experiment. This paper focuses on the dynamics of the formation and erasure processes of the holographic gratings. Both the writing and erasure times exhibit sublinear dependencies on the illumination power intensity, which is a result of the sublinear photoconductivity of the material. The dependence of the rise time on the applied electric field is attributed to the field dependence of both the photocharge generation quantum efficiency and the charge mobility in the polymer matrix.

Zhang, Yue; Spencer, Christopher A.; Ghosal, Saswati; Casstevens, Martin K.; Burzynski, Ryszard

1994-09-01

179

Time-resolved digital holographic microscopy of laser-induced forward transfer  

NASA Astrophysics Data System (ADS)

We develop a method for time-resolved digital holographic microscopy to obtain time-resolved 3-D deformation measurements of laser-induced forward transfer (LIFT) processes. We demonstrate nanometer axial resolution and nanosecond temporal resolution of our method which is suitable for measuring dynamic morphological changes in LIFT target materials. Such measurements provide insight into the early dynamics of the LIFT process and a means to examine the effect of laser and material parameters on LIFT process dynamics.

Ma, H.; Venugopalan, V.

2013-06-01

180

The photodissociation and reaction dynamics of vibrationally excited molecules. Technical progress report, 1993--1994  

SciTech Connect

Combined vibrational overtone excitation and laser induced fluorescence detection was used to study dissociation dynamics of hydroxylamine (NH{sub 2}OH), laser induced grating experiments on water were analyzed, discovering the important role that electrostriction and thermal relaxation play, and a new apparatus for preparing vibrationally excited molecules with simulated Raman excitation was completed and the first measurements made. Role of vibrational excitation in photodissociation dynamics was studied using a vibrational state preparation technique, such as vibrational overtone excitation or stimulated Raman excitation, to create molecules with particular nuclear motions and then excite that molecule to a dissociative electronic state. Because the vibrational excitation alters the dissociation dynamics in the excited state, both by providing access to different portions of the excited state surface and by altering the motion of the system on the surface, it is usually refered to as vibrationally mediated photodissociation.

Not Available

1994-04-01

181

Femtosecond laser-induced breakdown in water  

NASA Astrophysics Data System (ADS)

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

Schaffer, Chris B.

1997-04-01

182

Dynamic Holographic Gratings in Methyl Red-Doped Nematic Liquid Crystals  

NASA Astrophysics Data System (ADS)

Orientational photorefractivity in liquid crystals doped with azo dye MR crystals is studied. The experiments are carried out with no voltage applied. Dynamic behavior and its dependence on writing beams intensity are presented. When excited by light, the dye tends to bond to the cell surface. Such an effect is irreversible and leads to the permanent component formation in diffracted signal. This is not beneficial for applications where change of written information is required (OASLMs, dynamic holography, all-optical switching). The process was strongly suppressed and was virtually eliminated for the light intensities used, by the choice of materials for alignment surfaces.

Ruzak, O.; Collings, N.; Crossland, W. A.; Wilkinson, T. D.; Davey, A. B.; Khoo, I. C.

183

Collapse and rebound of a laser-induced cavitation bubble  

NASA Astrophysics Data System (ADS)

A strong laser pulse that is focused into a liquid produces a vapor cavity, which first expands and then collapses with subsequent rebounds. In this paper a mathematical model of the spherically symmetric motion of a laser-induced bubble is proposed. It describes gas and liquid dynamics including compressibility, heat, and mass transfer effects and nonequilibrium processes of evaporation and condensation on the bubble wall. It accounts also for the occurrence of supercritical conditions at collapse. Numerical investigations of the collapse and first rebound have been carried out for different bubble sizes. The results show a fairly good agreement with experimental measurements of the bubble radius evolution and the intensity of the outgoing shock wave emitted at collapse. Calculations with a small amount of noncondensable gas inside the bubble show its strong influence on the dynamics.

Akhatov, I.; Lindau, O.; Topolnikov, A.; Mettin, R.; Vakhitova, N.; Lauterborn, W.

2001-10-01

184

Laser-induced regeneration of cartilage  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

185

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

186

Polarization properties in two wave mixing with moving grating in photorefractive BSO crystals - Application to dynamic interferometry  

Microsoft Academic Search

The polarization properties of the volume gratings in photorefractive B12SiO20 crystals permit to increase the contrast and signal to noise ratio in the image plane of a large size vibrating object structure. The experiment is based on the nearly degenerate two wave mixing of a pump beam with a low intensity signal beam due to the object structure (moving grating

J. P. Herriau; J. P. Huignard; A. G. Apostolidis; S. Mallick

1985-01-01

187

Planar laser induced fluorescence in aqueous flows  

Microsoft Academic Search

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

J. P. Crimaldi

2008-01-01

188

Fiber grating sensors  

Microsoft Academic Search

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

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

1997-01-01

189

Design of high-efficiency dielectric reflection gratings  

SciTech Connect

We discuss examples of designs for all-dielectric reflection gratings that tolerate high intensity and are potentially capable of placing up to 99{percent} of the incident light into a single diffraction order, such as are needed for contemporary high-power lasers utilizing chirped-pulse amplification. The designs are based on placing a dielectric transmission grating atop a high-reflectivity (HR) multilayer dielectric stack. We comment on the connection between transmission gratings and reflection gratings and note that the grating and the HR stack can, to a degree, be treated independently. Because many combinations of gratings and multilayer stacks offer high efficiency, it is possible to attain secondary objectives in the design. We describe examples of such designs aimed toward improving fabrication and lowering the susceptibility to laser-induced damage. We present examples of the dependence of grating efficiency on grating characteristics. We describe examples of high-efficiency (95{percent}) gratings that we have fabricated by using hafnia and silica multilayers. {copyright} 1997 Optical Society of America

Shore, B.W.; Perry, M.D.; Britten, J.A.; Boyd, R.D.; Feit, M.D.; Nguyen, H.T.; Chow, R.; Loomis, G.E. [Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94550 (United States); Li, L. [Optical Sciences Center, University of Arizona, Tucson, Arizona 85721 (United States)

1997-05-01

190

Observation of nanoparticle formation process by two-dimensional laser-induced fluorescence, UV Rayleigh scattering, and re-decomposition laser-induced fluorescence methods  

Microsoft Academic Search

We have investigated the formation process of nanoparticles in the laser ablation plume by different laser imaging spectroscopy techniques, such as Two-Dimensional laser induced fluorescence (2D-LIF), UV Rayleigh scattering (UV- RS), and Re-Decomposition LIF (ReD-LIF). Clusters, which are hardly observed by the UV-RS method due to their small size, are observed by the ReD-LIF method. The dynamics and formation processes

Junichi Muramoto; Takahiro Inmaru; Yoshiki Nakata; Tatsuo Okada; Mitsuo Maeda

2000-01-01

191

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

192

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

193

Femtosecond laser induced breakdown for combustion diagnostics  

NASA Astrophysics Data System (ADS)

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

Kotzagianni, M.; Couris, S.

2012-06-01

194

Influence of the Glass-Transition Temperature and the Chromophore Content on the Grating Buildup Dynamics of poly(N-vinylcarbazole)-based Photorefractive Polymers.  

PubMed

The influence of the glass-transition temperature T(g) and the electro-optical chromophore content on the grating buildup dynamics in photorefractive polymer composites is investigated. The response times were found to be strongly dependent on both parameters. In the low-T(g) regime, composites of different chromophore content respond similarly quickly (200-500 ms), whereas significant differences occur for T(g) above the measurement (room) temperature. The composites with the highest chromophore content give the best steady-state performance; however, their response is much slower than that for those containing less chromophore. PMID:18273230

Bittner, R; Bräuchle, C; Meerholz, K

1998-05-10

195

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.

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

2012-01-01

196

Laser pulse induced gold nanoparticle gratings  

SciTech Connect

We report the results of our experimental investigation of laser induced gold nanoparticle gratings and their optical diffraction properties. A single shot of a pair Nd-YAG laser pulses with the same polarization is directed toward a 6 nm thick gold film on a substrate of polymethyl methacrylate. As a result of the laser illumination, the thin gold film is fragmented into an array of nanoparticles. Through the observation of scanning electron and dark-field optical microscopes, we discovered that the morphology of the gold nanoparticle grating is dependent on the fluence of laser pulse. The spectrum of first order diffraction shows the dependence on the absorbance property due to the presence of the nanoparticles. The ablation of nanothickness thin films via the use of laser pulses may provide a simple and efficient method for the fabrication of nanoscale structures, including two dimensional arrays of nanoparticles.

Hung, W.-C.; Cheng, W.-H. [Institute of Electro-Optical Engineering, National Sun Yat-sen University, Kaohsiung 804, Taiwan (China); Tsai, M.-S.; Chung, W.-C. [Department of Applied Physics, National Chiayi University, Chiayi 600, Taiwan (China); Jiang, I-M. [Department of Physics, National Sun Yat-sen University, Kaohsiung 804, Taiwan (China); Yeh, Pochi [Department of Electrical and Computer Engineering, University of California, Santa Barbara, California 93106-9560 (United States)

2008-08-11

197

Laser-induced ionization of Na vapor  

SciTech Connect

The production of Na/sub 2//sup +/ ions by off-resonant laser excitation in the 5800-6200A region mainly results from two-photon absorption by the Na/sub 2/ molecule to highly excited gerade states followed by (a) direct ionization by absorbing a third photon or (b) coupling to the molecular Na/sub 2/ D/sup 1/PI..mu.. Rydberg state which is subsequently ionized by absorbing a third photon. This mechanism, i.e., a two-photon resonance three photon ionization process, explains a recent experimental observation of Roussel et al. It is suggested that the very same mechanism is also responsible for a similar observation reported by Polak-Dingels et al in their work using two crossed Na beams. In the latter two studies the laser-induced associative ionization processes were reported to be responsible for producing the Na/sub 2//sup +/ ion. From the ratio of molecular to atomic concentration in the crossed beam experiment of Polak-Dingels et al we estimate that the cross section for producing Na/sub 2//sup +/ through laser-induced associative ionization is at least four orders of magnitude smaller than ionization through the two-photon resonance three photon ionization process in Na/sub 2/ molecules.

Wu, R.C.Y.; Judge, D.L.; Roussel, F.; Carre, B.; Breger, P.; Spiess, G.

1982-01-01

198

Laser interactions in fluid materials: laser-induced cavitation in liquid nitrogen and the possibility of environmental gas decomposition by laser  

NASA Astrophysics Data System (ADS)

Studies on some laser interactions to fluid materials are presented. Firstly, pulsed-laser-induced cavitation bubble in liquid nitrogen is investigated by YAG laser irradiation. High speed schlieren photographs by Imacon-790 are taken to observe the laser-induced bubble dynamics. Bubble and solid wall interactions are also investigated. Based on the results obtained, a novel laser surface processing technology using the pulse-laser-induced cavitation bubbles is secondly proposed. Furthermore, discussing by the fundamental results of the experiment of laser-gas molecular absorption, the possibility of decomposition of environmental gases by CW CO2 laser irradiation is also studied.

Maeno, Kazuo; Sato, Hitoshi; Prat, Christophe; Endo, Seiichi

1998-12-01

199

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

200

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

201

Radial variation of laser--induced air plasma parameters  

Microsoft Academic Search

Summary form only given. Laser induced breakdown spectroscopy (LIBS) is a noninvasive technique that needs no sample preparation and even recently, quantitative measurements were done without the need for calibration standards. Much research has been done on the laser induced air plasma to study the spatial variation of plasma parameters in the axial direction of the laser beam. In this

M. Mathuthu; R. Raseleka; A. Forbes

2006-01-01

202

Laser-Induced Distortions and Disturbance Propagation of Delocalized Electronic States in Monatomic Carbon Chains  

Microsoft Academic Search

Tight-binding electron-ion dynamics of carbon chains pumped by intense laser pulses are performed to study the interactions between monatomic carbon chains and lasers. Laser-induced distortions of carbon chains, which are enhanced by a long wavelength laser, are investigated. The carbon chains with a strong laser beam focused on one terminal are simulated to study the disturbance of electronic states. By

Yang Gong-Xian; Gong Xiu-Fang

2012-01-01

203

Interaction of laser-induced cavitation bubbles with composite surfaces  

NASA Astrophysics Data System (ADS)

The dynamics of a laser-induced cavitation bubble near a composite surface, consisting of either a thin rigid plate glued on a foam rubber (composite surface A) or a deformable rubber plate glued on a foam rubber (composite surface B), was investigated experimentally with high-speed photography. To understand the interaction between a cavitation bubble and a composite surface, the dynamic properties of the composite surfaces were measured with a modal analysis by providing a maximum frequency to 5 kHz, since the period of the bubble motion with the radius of 1 mm is about 200 ?s. It was found that bubble migration was significantly influenced by the dynamic property of composite surfaces, showing a range of response between the free surface and rigid boundary cases. For one of the composite surfaces with a deformable rubber, bubble splitting was generated for ?<1.1, where ?=L/Rmax with L being the initial bubble location and Rmax the maximum bubble radius. A neutral bubble collapse occurred at a specified bubble location defined as ?N that was fairly correlated with the compliance, Gn, of the composite surfaces. The value of ?N decreased with increasing Gn.

Tomita, Y.; Kodama, T.

2003-09-01

204

Dynamic strain measurements of a circular cylinder in a cross flow using a fibre Bragg grating sensor  

Microsoft Academic Search

A fibre Bragg grating (FBG) sensor was proposed as an alternative to strain gauges to measure the strain ? of a vibrating\\u000a cylinder in a uniform cross flow. In order to validate the measurements of the FBG sensor, the transverse fluctuating bending\\u000a displacement Y of the cylinder was also measured using a laser vibrometer. The two measurements were found to

Y. Zhou; R. M. C. So; W. Jin; H. G. Xu; P. K. C. Chan

1999-01-01

205

Laser-induced fluorescence-cued, laser-induced breakdown spectroscopy biological-agent detection  

SciTech Connect

Methods for accurately characterizing aerosols are required for detecting biological warfare agents. Currently, fluorescence-based biological agent sensors provide adequate detection sensitivity but suffer from high false-alarm rates. Combining single-particle fluorescence analysis with laser-induced breakdown spectroscopy (LIBS) provides additional discrimination and potentially reduces false-alarm rates. A transportable UV laser-induced fluorescence-cued LIBS test bed has been developed and used to evaluate the utility of LIBS for biological-agent detection. Analysis of these data indicates that LIBS adds discrimination capability to fluorescence-based biological-agent detectors.However, the data also show that LIBS signatures of biological agent simulants are affected by washing. This may limit the specificity of LIBS and narrow the scope of its applicability in biological-agent detection.

Hybl, John D.; Tysk, Shane M.; Berry, Shaun R.; Jordan, Michael P

2006-12-01

206

Surface relief gratings in azobenzene supramolecular systems based on polyimides  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

207

Laser induced fluorescence of dental caries  

NASA Astrophysics Data System (ADS)

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

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

208

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

209

Femtosecond laser-induced crystallization of amorphous Sb{sub 2}Te{sub 3} film and coherent phonon spectroscopy characterization and optical injection of electron spins  

SciTech Connect

A femtosecond laser-irradiated crystallizing technique is tried to convert amorphous Sb{sub 2}Te{sub 3} film into crystalline film. Sensitive coherent phonon spectroscopy (CPS) is used to monitor the crystallization of amorphous Sb{sub 2}Te{sub 3} film at the original irradiation site. The CPS reveals that the vibration strength of two phonon modes that correspond to the characteristic phonon modes (A{sub 1g}{sup 1} and E{sub g}) of crystalline Sb{sub 2}Te{sub 3} enhances with increasing laser irradiation fluence (LIF), showing the rise of the degree of crystallization with LIF and that femtosecond laser irradiation is a good post-treatment technique. Time-resolved circularly polarized pump-probe spectroscopy is used to investigate electron spin relaxation dynamics of the laser-induced crystallized Sb{sub 2}Te{sub 3} film. Spin relaxation process indeed is observed, confirming the theoretical predictions on the validity of spin-dependent optical transition selection rule and the feasibility of transient spin-grating-based optical detection scheme of spin-plasmon collective modes in Sb{sub 2}Te{sub 3}-like topological insulators.

Li Simian [State Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); Hebei Key Laboratory of Optoelectronic Information and Geo-detection Technology Shijiazhuang University of Economics, Shijiazhuang 050031 (China); Huang Huan; Wang Yang; Wu Yiqun; Gan Fuxi [Key Laboratory of High Power Laser Materials, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800 (China); Zhu Weiling; Wang Wenfang; Chen Ke; Yao Daoxin; Lai Tianshu [State Key Laboratory of Optoelectronic Materials and Technology, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China)

2011-09-01

210

Laser-induced cooling of a Yb:YAG crystal in air at atmospheric pressure.  

PubMed

We report for the first time the experimental demonstration of optical cooling of a bulk crystal at atmospheric pressure. The use of a fiber Bragg grating (FBG) sensor to measure laser-induced cooling in real time is also demonstrated for the first time. A temperature drop of 8.8 K from the chamber temperature was observed in a Yb:YAG crystal in air when pumped with 4.2 W at 1029 nm. A background absorption of 2.9 × 10-4 cm-1 was estimated with a pump wavelength at 1550 nm. Simulations predict further cooling if the pump power is optimized for the sample's dimensions. PMID:24150315

Filho, Elton Soares de Lima; Nemova, Galina; Loranger, Sébastien; Kashyap, Raman

2013-10-21

211

[Enhancement of the radiation of laser-induced stainless steel plasmas by prefabricated keyhole].  

PubMed

The prefabricated keyhole effects on the radiation characteristic of laser-induced stainless steel plasma were investigated. A high-energy neodymium glass pulse laser was used to ablate stainless steel sample in air at atmospheric pressure. Combined-type multi-function grating spectroscope and CCD spectral acquainting and processing system were used to record plasma spectrum. The electron temperature and the full width at half maximum of spectral line, respectively. The study results showed that the spectral intensity and signal-to-background ratio of laser plasma increase in the range of 71.5%-125.8% and 7.6%-18.5% respectively when a laser beam (-5 J) acted on the stainless steel sample on which prefabricated keyholes (d = 1.5 mm, h = 0.8 mm) were placed. The plasma temperature and electron density increased by about 1 200 K and 1.21 x 10(16) cm(-3), respectively. This proved that prefabricated keyhole had a significant enhancement effect on the radiation of laser-induced stainless steel plasma. PMID:22097827

Chen, Jin-Zhong; Yu, Shi-Juan; Sun, Jiang; Li, Xun; Wang, Chun-Sheng

2011-09-01

212

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

Microsoft Academic Search

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

Alexander Horn; Ilja MINGAREEV; Isamu MIYAMOTO

2006-01-01

213

Dynamics of perceptual bi-stability for stereoscopic slant rivalry and a comparison with grating, house-face, and Necker cube rivalry.  

PubMed

A way to study conscious perception is to expose the visual system to an ambiguous stimulus that instigates bi-stable perception. This provides the opportunity to study neural underpinnings related to the percepts rather than to the stimulus. We have recently developed a slant-rivalry paradigm that has beneficial metrical (quantitative) aspects and that exhibits temporal aspects of perceptual reversals that seemed to be under considerable voluntary control of the observer. Here we examined a range of different aspects of the temporal dynamics of the perceptual reversals of slant rivalry and we compared these with the dynamics of orthogonal grating rivalry, house-face rivalry, and Necker cube rivalry. We found that slant rivalry exhibits a qualitatively similar pattern of dynamics. The drift of the perceptual reversal rate, both across successive experimental repetitions, and across successive 35-s portions of data were similar. The sequential dependence of the durations of perceptual phases, too, revealed very similar patterns. The main quantitative difference, which could make slant rivalry a useful stimulus for future neurophysiological studies, is that the percept durations are relatively long compared to the other rivalry stimuli. In the paper that accompanies this paper [van Ee, R., van Dam, L. C. J., Brouwer, G. J. (2005). Voluntary control and the dynamics of perceptual bi-stability. Vision Research,] we focused on the role of voluntary control in the dynamics of perceptual reversals. PMID:15571736

van Ee, Raymond

2005-01-01

214

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

PubMed Central

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

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

2011-01-01

215

Novel laser-induced cavitation: the constrained ring bubble  

NASA Astrophysics Data System (ADS)

Using high speed photography at sub-microsecond temporal resolution, we observed laser-induced cavitation within a thin film of liquid. In accordance with the literature, focusing a pulse of a gaussian-like intensity distribution into the liquid, instigated a disk-shaped cavity. The propagation of an acoustic transient, generated during the formation and expansion of the cavity, is evidenced by secondary cavitation stimulated in the surrounding liquid. Introducing a laguerre-gauss holographic diffractive optic element into the beam path, re-distributes the optical energy into the socalled 'doughnut mode', with an axial intensity minimum. Focusing this modulated pulse into the liquid induced a ringshaped cavity with a notably different dynamic to that of the disk cavity, due primarily to the encapsulated droplet, which is present from cavity initiation through expansion and subsequent deflation. In this paper we present initial observations on the novel dynamics of the ring-shaped cavity and discuss several of the distinctive features. Particularly the secondary cavitation induced in the surrounding liquid, and the implicated multiplexing of the acoustic transient generated during the ring-cavity expansion, is of interest.

Prentice, Paul; Zolotovskaya, Svetlana; Rafailov, Edik

2010-02-01

216

Fiber grating spectra  

Microsoft Academic Search

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

T. Erdogan

1997-01-01

217

Molecular formation dynamics of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one, 1,3,5-trinitroperhydro-1,3,5-triazine, and 2,4,6-trinitrotoluene in air, nitrogen, and argon atmospheres studied using femtosecond laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

Femtosecond laser induced breakdown spectroscopic (LIBS) studies were performed on three high energy materials namely 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 2,4,6-trinitrotoluene (TNT). LIBS spectral features were obtained for these samples in three different atmospheres i.e. air, nitrogen, and argon. Different molecular to elemental ratios in these three atmospheres were investigated in detail. CN/C and CN/N ratios were observed to be prominent in nitrogen and air atmospheres. We attempt to elucidate the role of several reactions involving CN molecular formation in connection with discrepancies obtained in the measured ratios. The complete temporal dynamics of atomic C (247.82 nm) and CN (388.20 nm) molecular species in three different atmospheres are elaborated. The decay rates of C peak were found to be longest (96 ns-121 ns) in argon atmosphere for all the samples. The decay rates of CN peak (388.2 nm) were longer (161 ns-364 ns) in nitrogen compared to air and argon atmospheres. We also attempt to explicate the decay mechanisms with respect to the molecular species formation dynamics in different atmospheres.

Sreedhar, Sunku; Nageswara Rao, E.; Manoj Kumar, G.; Tewari, Surya P.; Venugopal Rao, S.

2013-09-01

218

Probing electron correlations by laser-induced tunnel ionization  

NASA Astrophysics Data System (ADS)

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

Staudte, André.

2011-03-01

219

Structural characterization of lamellar multilayer gratings by x-ray reflectivity and scanning electron microscopy  

Microsoft Academic Search

Structural characterization of a fully etched amorphous W\\/Si multilayer grating with lateral periodicity 800 nm is performed by x-ray reflectivity. Grating truncation rod profiles have been calculated using a matrix modal eigenvalue approach of the dynamical theory of reflectivity by gratings which generalizes the Fresnel transmission and reflection coefficients for lateral diffraction. The interface roughness in rough gratings has been

M. Jergel; P. Mikulík; E. Majková; S. Luby; R. Senderák; E. Pincík; M. Brunel; P. Hudek; I. Kostic; A. Konecníková

1999-01-01

220

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

SciTech Connect

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

Odulov, S.G.

1984-03-01

221

Continuous Wave Chemical Laser for Laser-Induced Fluorescence Studies.  

National Technical Information Service (NTIS)

Laser-induced fluorescence experiments have been accomplished with a newly developed cw chemical laser. The design and operating characteristics of this small-scale transverse flow chemical laser source are presented. The fluorescence measurement techniqu...

R. R. Stephens T. A. Cool

1971-01-01

222

Classical cutoffs for laser-induced nonsequential double ionization  

SciTech Connect

Classical cutoffs for the momenta of electrons ejected in laser-induced nonsequential double ionization are derived for the recollision-impact-ionization scenario. Such simple cutoff laws can aid in the interpretation of the observed electron spectra.

Milosevic, D.B. [Faculty of Science, University of Sarajevo, Zmaja od Bosne 35, 71000 Sarajevo (Bosnia and Herzegowina); Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin (Germany); Becker, W. [Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin (Germany)

2003-12-01

223

Intrinsic laser-induced breakdown of silicate glasses  

Microsoft Academic Search

This paper is a survey of experimental results in laser- induced damage observed mainly at State Optical Institute (St. Petersburg, Russia) and at School of Optics\\/CREOL (Orlando, FL) which expounds conditions of observation of an intrinsic breakdown of high-purity silicate glasses and proposes the general idea of its mechanism. It is shown that the surface laser-induced breakdown of dielectrics is

Leonid B. Glebov

2002-01-01

224

Laser-induced thermal acoustics: simple accurate gas measurements  

Microsoft Academic Search

Received February 17, 1994 Laser-induced thermal acoustics (LITA), an optical four-wave mixing technique, has been used for sensitive measurement of the sound speed, thermal diffusivity, acoustic damping rate, and complex susceptibility of a gas. In LITA, laser-induced acoustic waves scatter laser light into a coherent, modulated signal beam. A simple expression accurately describes the signal. Atmospheric sound speeds accurate to

E. B. Cummings

1994-01-01

225

Waveguide mode filter fabricated using laser-induced forward transfer  

Microsoft Academic Search

Titanium in-diffused lithium niobate index-tapered waveguides have been fabricated using laser-induced forward transfer technique for mode-filtering applications. Details of their fabrication, losses and transmission characterization are presented. OCIS codes: (140.3390) Laser materials processing; (140.7090) Ultrafast lasers; (220.4000) Microstructure fabrication; Laser-Induced Forward Transfer; (230.7370) Waveguides. In this paper we report the fabrication of titanium (Ti) in-diffused lithium niobate (LN) index-tapered waveguides

K. S. Kaur; A. Z. Subramanian; D. P. Banks; M. Feinaeugle; C. Y. J. Ying; C. L. Sones; S. Mailis; R. W. Eason

2011-01-01

226

Anisotropy of Laser-Induced Bulk Damage of Single Crystals  

Microsoft Academic Search

The regularities of laser-induced damage of anisotropic materials, such as LiNbO3 and KDP dielectric single crystals, are experimentally studied. It is revealed that the shape of laser-induced damage in the dielectric crystals depends on the elastic symmetry of crystal and the propagation direction of the laser beam. When the beam propagates along the optic axis of crystals, the figures of

O. Krupych; Ya. Dyachok; I. Smaga; R. Vlokh

2007-01-01

227

Toward standardization in laser-induced damage testing  

NASA Astrophysics Data System (ADS)

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

Seitel, Steven C.; Guenther, Karl H.

1986-01-01

228

Amorphous carbon film deposition by laser induced C 60 fragmentation  

Microsoft Academic Search

It is demonstrated that a pure carbon (fullerene) precursor, C60, is appropriate for laser-induced carbon film deposition. Amorphous carbon films were obtained on Si and SiO2 substrates upon ArF excimer laser induced fragmentation of gas phase C60. The depositions were performed in Ar and H2 ambient in a hot-wall reactor at 550°C. Strong C2 emission bands were observed by optical

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

1997-01-01

229

Influence of lattice heating time on femtosecond laser-induced strain waves in InSb  

NASA Astrophysics Data System (ADS)

Femtosecond laser-induced strain waves in InSb are studied by means of time-resolved x-ray diffraction. The temporal evolution of the measured x-ray diffracted intensity reveals that the lattice dynamics depends on the time scale of energy transfer from excited carriers to the lattice. A framework that accounts for this energy-transfer time (lattice heating time) is presented and applied to model the fluence dependence of the transient x-ray diffraction data. In this model the initial strain wave dynamics depends crucially on the lattice heating time, which decreases with increasing fluence.

Krasniqi, F. S.; Johnson, S. L.; Beaud, P.; Kaiser, M.; Grolimund, D.; Ingold, G.

2008-11-01

230

Femtosecond laser-induced periodic surface structures on silica  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

231

Nanoscale laser-induced forward transfer through patterned Cr films  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

232

Acoustic transient generation by holmium-laser-induced cavitation bubbles  

NASA Astrophysics Data System (ADS)

The acoustic effects of free-running 2.12 micron Cr:Tm:Ho:YAG laser pulses delivered in water are studied. Laser pulses of 10 to 1200 mJ energy and 230 microsecs duration (full width at half-maximum) are used. Delivery fiber diameters of 200 - 600 microns are investigated. Combined fast flash video imaging and needle probe hydrophone pressure sensing are used. The experimental results show that the laser-induced water vapor bubbles can generate strong acoustic transients at the bubble collapse several hundreds of microsecs after the start of the laser pulse. Pressures of up to 3600 bar are measured. Above a laser fluence threshold of 40 J/sq cm the pressure amplitude increases sharply, reaching a maximum value between 100 and 200 J/sq cm. At higher fluences up to more than 1000 J/sq cm, the pressure amplitude is found to decrease again. A two-phase mechanism is proposed to describe the complex bubble dynamics generated by the free-running pulses: The isotropic expansion of an initially superheated water volume is followed by a continuous ablation phase. The results suggest a mechanism of possible unwanted acoustic damage during Holmium laser medical applications in a liquid environment.

Asshauer, T.; Rink, K.; Delacretaz, G.

1994-11-01

233

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

NASA Astrophysics Data System (ADS)

We have successfully fabricated germanium immersion gratings with resolving power of 45,000 at 10 ?m by using a nano precision 3D grinding machine and ELID (ELectrolytic In-process Dressing) method. However the method spends large amount of machine times. We propose grooves shape with a new principle for a solid grating, which achieves high performance and lower cost. We have developed volume phase holographic (VPH) grisms with zinc selenide (ZnSe) prisms for spectrograph of the Subaru Telescope and the other telescopes. While a VPH grism with high index prisms achieves higher dispersion, diffraction efficiency of VPH grating decreases toward higher orders. A "quasi-Bragg grating" which inherits advantage of a VPH grating achieves high diffraction efficiency toward higher orders. Wavelength tuners with a pair of counter-rotation prisms for a VPH and quasi-Bragg grating obtain high diffraction efficiency over wide wavelength range. The novel immersion grating, VPH grism with high index prisms, quasi-Bragg grating and wavelength tuners dramatically reduce volumes of astronomical spectrographs.

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

2006-07-01

234

High spatial resolution in laser-induced breakdown spectroscopy of expanding plasmas  

NASA Astrophysics Data System (ADS)

We report a technique that is able to achieve high spatial resolution in the measurement of the temporal and spectral emission characteristics of laser-induced expanding plasmas. The plasma is imaged directly onto the slit of an imaging spectrograph coupled to a time-gated intensified camera, with the plasma expansion direction being parallel to the slit extension. In this way, a single hybrid detection system is used to acquire the spatial, spectral and temporal characteristics of the laser induced plasma. The parallel acquisition approach of this technique ensures a much better spatial resolution in the expansion direction, reproducibility and data acquisition speed than commonly obtained by sequential measurements at different distances from the target. We have applied this technique to study the laser-induced plasma in LiNbO3 and Bi12Ge1O20, revealing phenomena not seen in such detail with standard instruments. These include extreme line broadening up to a few nanometers accompanied by self-absorption near the target surface, as well as different ablation and expansion dynamics for the different species ejected. Overall, the high precision and wealth of quantitative information accessible with this technique open up new possibilities for the study of fundamental plasma expansion processes during pulsed laser ablation.

Siegel, J.; Epurescu, G.; Perea, A.; Gordillo-Vázquez, F. J.; Gonzalo, J.; Afonso, C. N.

2005-08-01

235

Diffractive coherence in multilayer dielectric gratings  

SciTech Connect

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

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

1995-05-26

236

Optimization of the optical near-field distribution of metal multilayer dielectric gratings for pulse compressors  

NASA Astrophysics Data System (ADS)

Metal multilayer dielectric gratings (MMDGs) for pulse compressors used in high-energy laser systems should enable high efficiency, as well as provide broad bandwidths and high laser-induced damage thresholds. The non-uniform optical near-field distribution of MMDGs is an important factor that limits damage resistance capabilities. The efficiency and electric field distributions of MMDGs with a corrugated SiO2 layer and operated at 800 nm are analyzed by rigorous coupled-wave analysis. The maximum electric field in the grating ridge, match layer, and metal layer decreases with increasing grating diffraction efficiency. High efficiency and a low electric field are obtained with a 90° slope angle in the grating ridge. The bandwidth and maximum electric field in the metal layer decrease with increasing high- and low-index material pairs, and the maximum electric fields in the grating ridge and match layer initially decrease and then increase. The peak electric field in the grating is optimized with a merit function; the optimization covers the enhancement of diffraction efficiency, bandwidth, and reduction of electric field. The bandwidth of the optimized MMDGs is 160 nm with a diffraction efficiency exceeding 90%. The largest electric field is modulated in air to obtain a low electric field and high laser-induced damage threshold.

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

2013-07-01

237

Laser-Induced Fluorescence Plasma Ion Diagnostics  

NASA Astrophysics Data System (ADS)

In nearly 25 years plasma laser-induced fluorescence (LIF) has evolved from proof-of-principle experiments.(R. Stern and J. Johnson, Phys. Rev. Lett. 34, 1548 (1975).) to using the latest advances in diodes lasers.(G.D. Severn, D.A. Edrich, and R. McWilliams, Rev. Sci. Instrum. 69, 10 (1998).) LIF can provide time- and space-resolved plasma ion distribution, f_i(x,v,t), measurements (typically on ?sec and mm scales) with velocity resolution of a few tens of m/sec. Via optical tagging instrumentation.(R.A. Stern, D.N. Hill, and N. Rynn, Phys. Lett. A93, 127 (1983).) diffusion and convection can be studied in real space and velocity space in quiet or turbulent plasmas.(R. McWilliams and M.K. Okubo, Phys. Fluids 30, 2849 (1987), R. McWilliams, M.K. Okubo, and N.S. Wolf, Phys. Fluids B2, 523 (1990), J. Bowles, R. McWilliams, and N. Rynn, Phys. Plasmas 1, 3814 (1994).) Non-Maxwellian multi-dimensional ion distributions can be studied by optical tomography.(M. Zintl and R. McWilliams, Rev. Sci. Instrum. 65, 2574 (1994).) Examples of LIF's flexibility are: diagnosis of tokamak plasma ions,(S.J. Sanders, P.M. Bellan, and R. Stern, Phys. Plasmas 5, 716 (1998).) measures of nonlinear propagation of ion structures,(G. Bachet, F. Skiff, M. Dindelegan, F. Doveil, and R.A. Stern, Phys. Rev. Lett. 80, 3260 (1998).) and helping in the design of plasma processing apparatus.(M. Goeckner, J. Goree, and T.E. Sheridan, Phys. Fluids B3, 2913 (1991).) This talk will present LIF diagnostic equipment for plasma physics ion measurements. While laser technology has broadened LIF usefulness there remain pitfalls to its application in some arenas. This tutorial adumbration is posted at http://HAL9000.ps.uci.edu .

McWilliams, Roger

1999-11-01

238

Bragg Grating Simulation Software.  

National Technical Information Service (NTIS)

This document is a user manual for a software application that predicts the complex reflection spectrum of fibre Bragg gratings, given user defined input parameters. The software is designed primarily to complement the joint DSTO/ Swinburne grating writin...

C. Brooks C. Davis

2008-01-01

239

Interaction between luminance gratings and disparity gratings  

Microsoft Academic Search

It was shown from geometry and photographic measurement that the shading pattern for a sinusoidal corrugated surface of frequency f approximates to a luminance-deé ned grating of frequency f, 2f or f C 2f in specié c relative phase. It was coné rmed that a luminance grating modié es the appearance of a suprathreshold stereoscopic corrugated surface, suggesting an interaction

Michael Wright; Tim Ledgeway

2004-01-01

240

All-fiber dynamic gain equalizer based on a twisted long-period grating written by high-frequency CO2 laser pulses.  

PubMed

A novel dynamic gain equalizer for flattening Er-doped fiber amplifiers based on a twisted long-period fiber grating (LPFG) induced by high-frequency CO(2) laser pulses is reported for the first time to our knowledge. Experimental results show that its transverse-load sensitivity is up to 0.34 dB/(g.mm(-1)), while the twist ratio of the twisted LPFG is approximately 20 rad/m, which is 7 times higher than that of a torsion-free LPFG. In addition, it is found that the strong orientation dependence of the transverse-load sensitivity of the torsion-free LPFG reported previously has been weakened considerably. Therefore such a dynamic gain equalizer based on the unique transverse-load characteristics of the twisted LPFG provides a much larger adjustable range and makes packaging of the gain equalizer much easier. A demonstration has been carried out to flatten an Er-doped fiber amplifier to +/-0.5 dB over a 32 nm bandwidth. PMID:17228383

Zhu, T; Rao, Y J; Wang, J L

2007-01-20

241

Analysis of nonuniform gratings  

Microsoft Academic Search

It has been shown earlier that the launching of gap solitons into nonuniform nonlinear Bragg gratings can be significantly easier than for uniform nonlinear Bragg gratings. In this paper we examine a variety of simple nonuniform Bragg gratings and compare their suitability for the launching process, by studying the positions of the zeros of the reflection spectrum.

Neil G. R. Broderick; C. Martijn de Sterke

1995-01-01

242

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

243

Pulsed laser-induced evaporation of liquids and its applications  

NASA Astrophysics Data System (ADS)

The interaction of laser irradiation with materials is very important in a variety of laser-based manufacturing processes and scientific studies. Particularly, the interaction of a short laser pulse with absorbing liquids or solid materials in contact with liquid is central to a number of applications, including laser cleaning of microcontaminants, pulsed laser deposition of thin film materials, laser tissue removal, and laser surface texturing. In this dissertation, experimental and theoretical works on the following topics are summarized: (1) physical mechanisms of pulsed laser induced ablation of absorbing liquids at laser fluence below the plasma ignition threshold, (2) analysis of rapid vaporization at the absorbing solid/transparent liquid interface, (3) laser cleaning of surface contaminates. Concerning the first topic, the near-threshold ablation process at low laser fluences and the high power explosive vaporization process accompanying subsequent ablation plume dynamics are elucidated. Acoustic-wave detection by a piezoelectric pressure transducer, visualization by laser flash photography, and optical reflection/transmission measurements are carried out for the in-situ diagnosis of the process. Quantification of the acoustic-field generation and detection of the bubble-nucleation dynamics in the rapid vaporization at the solid liquid interface are performed by photoacoustic beam deflection technique and optical interferometry, respectively. Finally, experiments are carried out for the development of a practical laser cleaning tool and the analysis of the contaminant-removal mechanism. The results show that the near-threshold ablation by a short laser pulse is initiated by the tensile component of the thermoelastic stress without significant increase of liquid temperature at low laser fluences. On the other hand, if the heating rate is rapid enough to achieve high degree of superheating of the liquid, explosive vaporization takes place due to the abrupt increase of homogeneous-bubble-nucleation rate. This mechanism then plays the major role in the ablation dynamics. In the case of low-power gradual heating, ablation is largely an isobaric thermal vaporization process, initiated at the saturation temperature. Pulsed laser induced vaporization of liquid at the solid/liquid interface occurs with a high degree of superheating of liquid. Enhancement in the acoustic energy conversion efficiency is observed due to the rapid bubble growth in the initial stage. The pressure measurements reveal that a compressive pressure wave packet is radiated from the water-solid interface with the peak intensity of the order of 1 MPa in the far field. Comparison of the results from interferomety with those from the optical reflectance and forward scattering measurements suggests that separate bubbles begin to grow in the early stage right after the laser-pulse irradiation and that they tend to coalesce in a later stage. The laser cleaning tests confirm that the acoustic field augmentation by explosive vaporization at the solid/liquid interface can be utilized to remove submicron-sized particles from solid surfaces. The result demonstrates the feasibility of successful implementation of laser cleaning technology in the industrial cleaning process for microcontaminant removal.

Kim, Dongsik

244

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

SciTech Connect

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

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

1981-09-15

245

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

PubMed

The airborne laser-induced spectral emission bands obtained simultaneously from water Raman backscatter and the fluorescence of chlorophyll and other naturally occurring waterborne pigments are reported here for the first time. The importance of this type data lies not only in its single-shot multispectral character but also in the application of the Raman line for correction or calibration of the spatial variation of the laser penetration depth without the need for in situ water attenuation measurements. The entire laser-induced fluorescence and Raman scatter emissions resulting from each separate 532-nm 10-nsec laser pulse are collected and spectrally dispersed in a diffraction grating spectrometer having forty photomultiplier tube detectors. Results from field experiments conducted in the North Sea and the Chesapeake Bay/Potomac River are presented. Difficulties involving the multispectral resolution of the induced emissions are addressed, and feasible solutions are suggested together with new instrument configurations and future research directions. PMID:20333121

Hoge, F E; Swift, R N

1981-09-15

246

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

247

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

248

Dynamic Bending Rigidity of a 200-bp DNA in 4 mM Ionic Strength: A Transient Polarization Grating Study  

Microsoft Academic Search

DNA may exhibit three different kinds of bends: 1) permanent bends; 2) slowly relaxing bends due to fluctuations in a prevailing equilibrium between differently curved secondary conformations; and 3) rapidly relaxing dynamic bends within a single potential-of-mean-force basin. The dynamic bending rigidity (?d), or equivalently the dynamic persistence length, Pd=?d\\/kBT, governs the rapidly relaxing bends, which are responsible for the

Alexei N. Naimushin; Bryant S. Fujimoto; J. Michael Schurr

2000-01-01

249

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

PubMed

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

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

2011-10-01

250

Plume splitting and rebounding in a high-intensity CO2 laser induced air plasma  

NASA Astrophysics Data System (ADS)

The dynamics of plasma plume formed by high-intensity CO2 laser induced breakdown of air at atmospheric pressure is investigated. The laser wavelength is 10.6 ?m. Measurements were made using 3 ns gated fast photography as well as space and time resolved optical emission spectroscopy. The behavior of the plasma plume was studied with a laser energy of 3 J and 10 J. The results show that the evolution of the plasma plume is very complicated. The splitting and rebounding of the plasma plume is observed to occur early in the plumes history.

Chen, Anmin; Jiang, Yuanfei; Liu, Hang; Jin, Mingxing; Ding, Dajun

2012-07-01

251

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

252

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

SciTech Connect

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

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

2006-04-24

253

Laser induced bunch lengthening on the ACO storage ring FEI  

NASA Astrophysics Data System (ADS)

Laser induced bunch lengthening has been measured on the ACO storage ring FEL. The experimental data at low current generally confirms the existing theoretical models, while the high current data is dominated by anomalous effects. As part of the LURE/Stanford Free Electron Laser Project at Orsay, France, we have developed a sensitive method to measure the laser induced change in the electron bunch length. This method is capable of measuring the absolute bunch with a precision of 1%, and fractional changes in electron bunch length as small as 1 part in 100,000. Using this system, we have measured the steady state and time dependent laser induced bunch lengthening as a function of electron current, external laser intensity, RF cavity voltage, the undulator magnetic field, and the detection frequency.

Robinson, K. E.; Deacon, D. A. G.; Velghe, M. F.; Madey, J. M.

1982-09-01

254

Analysis of corroded glasses by laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

In the present work, the possibilities of application of laser-induced breakdown spectroscopy for the diagnosis and analysis of uncorroded and artificially weathered glasses have been studied. Optimization of the laser-induced breakdown spectroscopy parameters included the energy per pulse and number of pulses. Analysis of spectra allowed the identification, not only of the major components but also of the chromophores of the glass samples considered. Stratigraphic analyses, performed by applying successive laser pulses on the same spot, allowed the detection of the different corrosion layers built up during weathering (corrosion crust, gel layer and unaltered glass bulk). Finally, the comparison of the laser-induced breakdown spectroscopy results with the conventional techniques Scanning Electron Microscopy/Energy Dispersive X-ray analysis, X-ray fluorescence and ultraviolet-visible spectroscopy revealed the advantages of this spectroscopic technique for the practice of glass conservation.

Carmona, N.; Oujja, M.; Rebollar, E.; Römich, H.; Castillejo, M.

2005-08-01

255

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

256

Review of long period fiber gratings written by CO2 laser  

NASA Astrophysics Data System (ADS)

This paper presents a systematic review of long period fiber gratings (LPFGs) written by the CO2 laser irradiation technique. First, various fabrication techniques based on CO2 laser irradiations are demonstrated to write LPFGs in different types of optical fibers such as conventional glass fibers, solid-core photonic crystal fibers, and air-core photonic bandgap fibers. Second, possible mechanisms, e.g., residual stress relaxation, glass structure changes, and physical deformation, of refractive index modulations in the CO2-laser-induced LPFGs are analyzed. Third, asymmetrical mode coupling, resulting from single-side laser irradiation, is discussed to understand unique optical properties of the CO2-laser-induced LPFGs. Fourthly, several pretreament and post-treatment techniques are proposed to enhance the efficiency of grating fabrications. Fifthly, sensing applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based temperature, strain, bend, torsion, pressure, and biochemical sensors. Finally, communication applications of the CO2-laser-induced LPFGs are investigated to develop various LPFG-based band-rejection filters, gain equalizers, polarizers, and couplers.

Wang, Yiping

2010-10-01

257

Physical model for the laser induced forward transfer process  

NASA Astrophysics Data System (ADS)

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

Röder, Tobias C.; Köhler, Jürgen R.

2012-02-01

258

Laser Induced Material Modification in the Bulk KDP Crystals  

SciTech Connect

Laser induced material modifications in the bulk and on the surface of KDP (KH{sub 2}PO{sub 4}) and DKDP (70-80% deuterated KDP) are studied using fluorescence imaging and spectroscopy. Photoluminescence is observed at damaged regions following above threshold exposure with an emission peak centered at 550-nm. In addition, surfaces exposed to >100 high power, 355-nm laser pulses reveal a reduced surface finishing quality as evidenced by an associated emission under UV photoexcitation. The emission spectra from the laser-induced damage sites and the laser degraded surfaces are similar suggesting the generation of similar defect species.

Radousky, H.B.; Staggs, M.; Runkel, M.; Burnham, A.

1999-12-16

259

Femtosecond laser induced surface melting and nanojoining for plasmonic circuits  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

260

Ultraviolet laser filaments for remote laser-induced breakdown spectroscopy (LIBS) analysis: applications in cultural heritage monitoring  

NASA Astrophysics Data System (ADS)

We report experiments with subpicosecond UV laser filaments for the remote analysis of samples related to objects of cultural heritage. The classic laser-induced breakdown spectroscopy (LIBS) technique finds new avenues through femtosecond filamentation, and dynamic remote LIBS becomes possible. Advantages such as self-regulated laser intensity deposition on the target suggest that there is significant potential for using UV femtosecond filaments for the remote analysis of sculpture and large monuments.

Tzortzakis, Stelios; Anglos, Demetrios; Gray, David

2006-04-01

261

Simulations of the femtosecond laser-induced desorption of CO from Cu(100) at 0.5 ML coverage  

Microsoft Academic Search

Simulations of the femtosecond laser-induced desorption of CO from Cu(100) at an initial temperature of 95K are reported, employing molecular dynamics with electronic frictions. Results are obtained for saturation (0.5 ML) CO coverage, which are compared with additional simulations in the zero coverage limit. In both cases, the desorption yield depends nonlinearly on laser fluence, with initial nonadiabatic energy flow

Clayton Springer; Martin Head-Gordon

1996-01-01

262

Laser-Induced Iodine Fluorescence Applied to Confined Supersonic Mixing  

Microsoft Academic Search

A laser-induced fluorescence (LIF) measurement system is presented and applied to the study of supersonic gas flows at low density. The LIF technique uses atomic or molecular tracers instead of microscopic particles so that particle lag effects, which are remarkable in low density flows, are avoided. The fluorescence signal of laser- excited molecules provides information about the gas velocity, temperature

Marc Havermann

263

Luminescence Spectra of Laser-induced Cavitation Bubbles  

Microsoft Academic Search

The luminescence spectra of laser-induced cavitation bubbles near rigid boundaries are measured for various relative distances between the bubble and the boundaries. We find that the luminescence spectra of bubbles collapsing near a single boundary consist of only a blackbody continuum. Luminescence from bubbles collapsing between two parallel rigid boundaries also contains OH* emission bands similar to those found in

Emil A. Brujan

2005-01-01

264

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

265

Expansion and radiative cooling of the laser induced plasma  

Microsoft Academic Search

To study the expansion and cooling process of the laser induced plasma generated by nanosecond pulsed laser ablation, experiments have been conducted which measure the position of the external shockwaves and the temperature of the vapor plumes. The positions of external shockwaves were determined by a femtosecond laser time-resolved imaging system. Vapor plume temperature was determined from spectroscopic measurements of

Sy-Bor Wen; Xianglei Mao; Chunyi Liu; Ralph Greif; Richard Russo

2007-01-01

266

Development of a laser-induced cell lysis system  

Microsoft Academic Search

A novel cell lysis system was developed that is based on laser-induced disruption of bacterial and yeast cells. It will find application as a rapid, efficient and clean sample preparation step in bioanalytical detection systems. Using E. coli as our model analyte, we optimized cell lysis with respect to optimal laser wavelength, lowest energy input requirements, RNA release from the

Mohit D. Dhawan; Frank Wise; Antje J. Baeumner

2002-01-01

267

Simulation and characterization of laser induced deformation processes  

Microsoft Academic Search

Laser induced deformation processes include laser forming (LF) and laser shock processing. LF is a recently developed and highly flexible thermal forming technique, and laser shock processing is an innovative mechanical process in which shock waves up to 10GPa are generated by a confined laser ablation process. The generated high pressure imparts beneficial residual stress into the surface layer of

Yajun Fan

2006-01-01

268

Diagnostics of oil pollution by laser-induced fluorescence  

Microsoft Academic Search

A novel method of laser-induced time-resolved fluorosensing has been developed in the laboratory. From the results of indoor experiments, a simulation outdoor facility has been built. Some significant achievements of the investigations are presented. A prototype of the airborne laser fluorosensor has been developed; its concept is supported by the reported results

P. Camagni; G. Colombo; C. Koechler; A. Pedrini; N. Omenetto; G. Rossi

1988-01-01

269

Hyperspectral laser-induced fluorescence imaging for assessing apple quality  

Technology Transfer Automated Retrieval System (TEKTRAN)

Chlorophyll fluorescence is useful for assessing fruit postharvest quality and condition. The objective of this research was to investigate the potential of using hyperspectral imaging to measure laser induced fluorescence for assessing apple fruit quality. A blue laser of 408 nm was used as an exci...

270

Laser-induced fluorescence imaging for studies of cultural heritage  

Microsoft Academic Search

Laser-induced fluorescence for remote imaging of historical monuments is an established technique, which in this work has been used in measurement campaigns at the Coliseum and the Baptistery of San Giovanni in Laterano in Rome, Italy. The results presented here are examples that show that biodeteriogens can be monitored and that materials can be identified. Also, cleaned and soiled areas

Rasmus Grönlund; Sune Svanberg; Jenny Hällström; Kerstin Barup; Giovanna Cecchi; Valentina Raimondi; David Lognoli; Lorenzo Palombi

2007-01-01

271

Laser-induced material modification in the bulk KDP crystals  

Microsoft Academic Search

Laser induced materials modifications in the bulk and on the surface of KDP and DKDP are studied using fluorescence image and spectroscopy. Photoluminescence is observed at damaged regions following above threshold exposure with an emission peak centered at 550-nm. In addition, surfaces exposed to > 100 high power, 355-nm laser pulse reveal a reduced surface finishing quality as evidenced by

Stavros G. Demos; Harry B. Radousky; Michael C. Staggs; Michael Runkel; Alan K. Burnham

2000-01-01

272

Excimer laser induced surface nitriding of aluminium alloy  

Microsoft Academic Search

This study describes a technique for the growth of thin nitride layer on aluminium alloy samples by direct laser synthesis with the advantages of good adhesion and localisation. The laser irradiation process is performed using an XeCl excimer laser (?=308 nm, 50 Hz) under a nitrogen atmosphere. The laser induced plasma interacts with the melted sample surface resulting in nitrogen

E. Sicard; C Boulmer-Leborgne; T Sauvage

1998-01-01

273

Novel laser induced interaction profiles in clusters of mesoscopic particles  

Microsoft Academic Search

We show that clusters of polarizable particles can form one or more equilibrium configurations in the presence of a laser field, with an equilibrium distance that depends sensitively on the frequency. The binding energy of these laser induced states scales with the particle volume and laser power making it possible to control by illumination the speed of agglomeration of weakly

F. Claro; R. Rojas

1994-01-01

274

Evaluation of oil spills by laser induced fluorescence spectra  

NASA Astrophysics Data System (ADS)

A low cost modular system for automatic oil spill detection, based on laser induced fluorescence light detection and ranging (LIF LIDAR) technology, which may be installed aboard watercraft and used for intensive surveillance of harborages, rivers, channels, and coastal waters, is described. First experimental results obtained with the developed LIF LIDAR detector prototype in the laboratory conditions are reported.

Utkin, Andrei B.; Lavrov, Alexander; Vilar, Rui

2010-09-01

275

Selectively electrical deposition copper on UV laser induced polyimide  

Microsoft Academic Search

With the rapid growth of miniaturization in the electronics industry, the electronics manufacturer are improving their packaging and assembly technique using the precise and high photon energy of laser process. Recent reports showed that the conductivity of some polymers such as PI can be increased up to 16 orders of magnitude by UV laser. However, the conductivity of laser induced

G. Zhao; H. M. Phillips; H. Zheng; S. C. Tam; W. Liu; G. Wen; Z. Gong

2000-01-01

276

Search for neutron emission in laser-induced cavitation  

NASA Astrophysics Data System (ADS)

Laser-induced cavitation bubbles in heavy water are investigated at different parameter settings. Neutrons are searched for in close temporal proximity to cavitation luminescence flashes with an estimated detection efficiency of 4%. No neutrons in coincidence with cavitation luminescence have been detected. This yields an upper limit of emitted neutrons per bubble collapse of 5 × 10-4.

Geisler, R.; Schmidt-Ott, W.-D.; Kurz, T.; Lauterborn, W.

2004-05-01

277

Laser-Induced Homoepitaxial Growth of Gallium Arsenide Films.  

National Technical Information Service (NTIS)

Epitaxial gallium arsenide films have been deposited on single crystalline GaAs substrates of (100) orientation at 425-500 C by ArF excimer laser-induced metalorganic chemical vapor deposition. The important process parameters include the cleanliness of t...

S. S. Chu T. L. Chu

1988-01-01

278

Temporal behavior of the wall voltage in a surface-type alternating current plasma display panel cell using laser induced fluorescence spectroscopy  

Microsoft Academic Search

Electric fields were measured using laser induced fluorescence spectroscopy and the wall voltage was estimated from the measured electric fields in a surface-type alternating current plasma display panel cell with a helium discharge (100 Torr) driven by square sustaining pulses. The wall voltage showed very complicated, temporally dynamic behavior. The polarity of the wall voltage changed rapidly as soon as

Jung Hun Kim; Jun Hak Lee; Ki-Woong Whang; Young Wook Choi

2001-01-01

279

Collective Spin Hall Effect for Electron-Hole Gratings  

NASA Astrophysics Data System (ADS)

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

Shen, Ka; Vignale, G.

2013-09-01

280

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

281

Laser applications to fluid materials: laser-induced cavitation in cryogenic liquid and gas decomposition by laser  

NASA Astrophysics Data System (ADS)

In this paper laser applications to fluid dynamical problems are presented. Firstly as for the recent research on cavitations, pulsed-laser-induced cavitation bubble in liquid nitrogen is studied. The bubble is produced by focused and pulsed irradiation of second harmonics of YAG laser in the cryostat. The dynamics of laser-induced bubble is visualized by high-speed shadowgraphs and schlieren photographs by an image-converter camera (Imacon-790). Bubble and solid wall interactions are also investigated. Based on the results obtained, a novel laser surface processing technology using the pulse-laser-induced cavitation bubbles is secondly proposed. The possibility of cold material surface processing by produced cavitation bubble is discussed including the cryogenic range. Furthermore, discussing by the fundamental results of the experiment of laser-gas molecular absorption, the possibility of decomposition of environmental gases by strong CW CO2 laser irradiation is also studied. Freon 12, 113, and other environmental gases including SF6 are very tough to be decomposed, and they break effectively the ozone molecules at high altitude above the Earth, or they heat up the earth. The wavelength range of the infrared laser is suitable for the molecular absorption to increase their temperature to be ionized. The possibility and trial experiments are discussed.

Maeno, Kazuo; Sato, Hitoshi; Endo, Seiichi

1999-05-01

282

Simulation of laser speckle reduction by using an array of diffraction gratings  

Microsoft Academic Search

An array of diffraction gratings and a Random Phase Plate (RPP) are used to suppress laser speckle effect. Dynamic diffraction spots are generated on the surface of the RPP, after which the scattering lights are perceived by a detector. Speckle Contrast Ratio (CR) and Number of Independent Speckle Patterns (NISP) with different gratings rotation orientations (theta), gratings frequencies (grooves per

Z. M. Tong; G. M. Ouyang; W. H. Gao; M. N. Akram; V. Kartashov; K. Y. Wang; X. Y. Chen

2010-01-01

283

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

284

Laser-induced multi-energy processing in diamond growth  

NASA Astrophysics Data System (ADS)

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

Xie, Zhiqiang

285

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

286

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

287

Laser-Induced Fluorescence of Isobutoxy in Competition with Ground State Decomposition.  

PubMed

Spectroscopic detection is an important method to monitor alkoxy radicals in atmospheric photochemistry studies. In this work, we report the first observation of the laser-induced fluorescence (LIF) spectra of isobutoxy, 2-methyl-1-butoxy, and 3-methyl-1-butoxy in supersonic jet-cooled condition. Ground state unimolecular decomposition and isomerization as well as excited state relaxation dynamics of isobutoxy were discussed in combination with the theoretical calculations. Analysis of the experimental and theoretical results showed that methyl substitution on the ? carbon of the alkoxy radicals changed the LIF spectra of alkoxy radicals significantly. The competition between the ground state reactions and the photoexcitation process depended strongly on the radical structure and hence affected the involvement of alkoxy radicals in the photochemical reactions in the upper troposphere. This study will help to understand the dynamic role of alkoxy radicals in the atmosphere. PMID:23617708

Liang, Gaiting; Liu, Chengxuan; Hao, Haiyan; Zu, Lily; Fang, Weihai

2013-05-01

288

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

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

289

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

PubMed

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

290

Laser-induced preferential dehydrogenation of graphane  

NASA Astrophysics Data System (ADS)

We have used first-principles simulations based on time-dependent density functional theory to show that short laser pulses can trigger preferential hydrogen desorption from the upper or lower side of suspended graphane (H-terminated graphene). This control is achieved by using intense ultrashort p-polarized laser pulses (˜2 fs) with an asymmetric time envelope. The dynamical Stark effect induced by the pulse creates an asymmetric charge distribution and force field on the H ions, even at low laser fluence. At finite temperatures the carbon-hydrogen stretching softens, favoring H desorption from one side. This transient geometry can be modified by halogen functionalization, which results in a two-dimensional dipolar structure.

Zhang, Hong; Miyamoto, Yoshiyuki; Rubio, Angel

2012-05-01

291

Laser induced trapping of excitons in coupled quantum wells  

NASA Astrophysics Data System (ADS)

Optical trapping and manipulation of neutral particles plays a major role in single particle studies in physics, chemistry, and biology [1]. An exciting recent outgrowth of the technique has been the experimental implementation of atom Bose- Einstein Condensation [2,3]. In this contribution, we report proposal and demonstration of laser induced trapping for a new system - a cold gas of excitons in coupled quantum wells. We report trapping a cold gas of excitons in laser induced traps and on the formation of a highly degenerate Bose gas of excitons in the trap. [1] A. Ashkin, IEEE Journal on Selected Items in Quantum Electronics/ 6, 841 (2000). [2] E. A. Cornell, C. E. Wieman, Rev. Mod. Phys./ 74, 875 (2002). [3] W. Ketterle, Rev. Mod. Phys./ 74, 1131 (2002).

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

2006-03-01

292

Laser-induced periodic surface structuring of biopolymers  

NASA Astrophysics Data System (ADS)

We report here on a systematic study about the formation of laser-induced periodic surface structures (LIPSS) on biopolymers. Self-standing films of the biopolymers chitosan, starch and the blend of chitosan with the synthetic polymer poly (vinyl pyrrolidone), PVP, were irradiated in air with linearly polarized laser beams at 193, 213 and 266 nm, with pulse durations in the range of 6-17 ns. The laser-induced periodic surface structures were topographically characterized by atomic force microscopy and the chemical modifications induced by laser irradiation were inspected via Raman spectroscopy. Formation of LIPSS parallel to the laser polarization direction, with periods similar to the laser wavelength, was observed at efficiently absorbed wavelengths in the case of the amorphous biopolymer chitosan and its blend with PVP, while formation of LIPSS is prevented in the crystalline starch biopolymer.

Pérez, Susana; Rebollar, Esther; Oujja, Mohamed; Martín, Margarita; Castillejo, Marta

2013-03-01

293

Europium speciation by time-resolved laser-induced fluorescence  

Microsoft Academic Search

Time-resolved laser-induced fluorescence has been used to investigate Eu complexes formed with a few main ligands encountered in natural waters: hydroxide, carbonate and humic substances. By varying pH and concentrations of ligands at fixed europium concentration and ionic strength, it was possible, together with free europium Eu3+, to identify spectrally and temporally carbonate complexes, namely Eu(CO3)+, Eu(CO3)2? and Eu(CO3)33? and

Gabriel Plancque; Valérie Moulin; Pierre Toulhoat; Christophe Moulin

2003-01-01

294

Laser induced damage in optical materials: 7th ASTM symposium  

Microsoft Academic Search

The Seventh ERDA-ASTM-ONR-NBS Symposium on Laser Induced Damage in Optical Materials was held at the National Bureau of Standards in Boulder, Colorado, on 29--31 July 1975. These Symposia are held as part of the activities in ASTM Subcommittee II on Lasers and Laser Materials, which is charged with the responsibilities of formulating standards and test procedures for laser materials, components,

A. J. Glass; A. H. Guenther

1976-01-01

295

Laser Induced Material Modification in the Bulk KDP Crystals  

Microsoft Academic Search

Laser induced material modifications in the bulk and on the surface of KDP (KHâPOâ) and DKDP (70-80% deuterated KDP) are studied using fluorescence imaging and spectroscopy. Photoluminescence is observed at damaged regions following above threshold exposure with an emission peak centered at 550-nm. In addition, surfaces exposed to >100 high power, 355-nm laser pulses reveal a reduced surface finishing quality

H. B. Radousky; M. Staggs; M. Runkel; A. Burnham

1999-01-01

296

Nanosecond-to-femtosecond laser-induced breakdown in dielectrics  

Microsoft Academic Search

We report extensive laser-induced damage threshold measurements on dielectric materials at wavelengths of 1053 and 526 nm for pulse durations Ï ranging from 140 fs to 1 ns. Qualitative differences in the morphology of damage and a departure from the diffusion-dominated Ϲ² scaling of the damage fluence indicate that damage occurs from ablation for Ïâ¤10 ps and from conventional melting,

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

1996-01-01

297

Ultratrace analysis of transuranic actinides by laser-induced fluorescence  

DOEpatents

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

Miller, Steven M. (Chelmsford, MA)

1988-01-01

298

Ultratrace analysis of transuranic actinides by laser-induced fluorescence  

DOEpatents

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

Miller, S.M.

1983-10-31

299

Multispectral-diode-laser-induced fluorescence biological particle sensor  

Microsoft Academic Search

Laser-induced fluorescence (LIF) provides a real-time technique for detecting micron-size airborne pathogens. Early LIF biological particle sensors used harmonic generation of UV in solid-state lasers to excite fluorescence. UV diode lasers have several key advantages over traditional lasers: a greater selection of wavelengths for the efficient and selective excitation of specific fluorescent biological compounds; continuous output so that all sampled

Geoffrey A. Wilson; Richard K. DeFreez

2004-01-01

300

Spectrally resolved laser-induced fluorescence for bioaerosols standoff detection  

Microsoft Academic Search

An efficient standoff biological warfare detection capability could become an important asset for both defence and security communities based on the increasing biological threat and the limits of the presently existing protection systems. Defence R&D Canada (DRDC) has developed, by the end of the 90s, a standoff bioaerosol sensor prototype based on intensified range-gated spectrometric detection of Laser Induced Fluorescence

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

2007-01-01

301

LASER-INDUCED DISSOCIATION OF MONOMERS AND DIMERS OF BROMINE  

SciTech Connect

In recent years various aspects of laser-induced processes in molecules have been studied. In our laboratory we used photofragrnent spectroscopy in order to probe excited states of bromine. The crossed laser and molecular beams experiment is described. The results on the monomer dissociation are discussed and compared with previous studies. In addition, the dissociation of dimers has been investigated for the first time using the same technique,and preliminary results are presented.

Sigrist, M.W.; Krajnovich, D.J.; Huisken, F.; Zhang, Z.J.; Lee, Y.T.; Shen, Y.R.

1980-05-01

302

Pressure Dependence of Laser-Induced Dielectric Breakdown in Water  

Microsoft Academic Search

The effects of pressure on laser-induced breakdown events at superthreshold irradiances in water were investigated over a range of pressures from 0 to 1380 bar. Breakdown events were generated using 5-ns Nd:YAG laser pulses of wavelength 532-nm. Observations of breakdown events were made using imaging and single detector techniques. Applications for use as a static and\\/or acoustic pressure sensor were

Jonathan Robert Sukovich; Ashwinkumar Sampathkumar; R. Glynn Holt

2011-01-01

303

Laser-induced shock wave effects on red blood cells  

Microsoft Academic Search

The trend for laser-based medical therapies has been towards short- pulse, high-peak power lasers. A consequence of using these lasers is the production of pressure waves that may propagate deep into tissue. Our previous experiments have concentrated on describing these effects and examining methods for measuring laser-induced shock waves. These two approaches were combined to study the effects of well-defined

Thomas J. Flotte; Joan K. Frisoli; Margaret Goetschkes; Apostolos G. Doukas

1991-01-01

304

Laser induced optical activity in the region of autoionizing states  

Microsoft Academic Search

Optical activity of atomic medium in the region of laser coupled autoionizing states is studied theoretically. Analytical expressions and numerical results are obtained for the laser induced polarization rotation angle and the acquired ellipticity of the VUV radiation in the region of the He 2s2p1P autoionizing state (60.13 eV) coupled by circularly polarized laser field with the 2p2 1S or

E. V. Gryzlova; A. N. Grum-Grzhimailo; A. I. Magunov; S. I. Strakhova

2008-01-01

305

Forensic comparative glass analysis by laser-induced breakdown spectroscopy  

Microsoft Academic Search

Glass samples of four types commonly encountered in forensic examinations have been analyzed by laser-induced breakdown spectroscopy (LIBS) for the purpose of discriminating between samples originating from different sources. Some of the glass sets were also examined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Refractive index (RI) measurements were also made on all glass samples and the refractive index data

Candice M. Bridge; Joseph Powell; Katie L. Steele; Michael E. Sigman

2007-01-01

306

Excimer laser induced etching of InP  

Microsoft Academic Search

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

V. M. Donnelly; T. R. Hayes

1990-01-01

307

Experimental and Numerical Study of Laser-Induced Forward Transfer Printing of Liquids  

NASA Astrophysics Data System (ADS)

Laser-induced forward transfer (LIFT) is an emerging high-resolution printing technique, which can deposit a wide range of fluid materials without a nozzle. In this process, a pulsed laser initiates the highly directed expulsion of fluid from a thin donor ink film onto a confined region of an acceptor substrate. Despite being validated as a versatile technique for printing devices, the fundamental mechanisms of the deposition process are still not fully understood. Further investigation of the laser-induced ejection dynamics is necessary in order to motivate new ways in which to optimize and control the printing process. Additionally, the LIFT configuration presents a unique laboratory in which to study novel regimes of fluid dynamics. This thesis presents an in-depth study of the LIFT printing process using a balance of experimental measurement and computational modeling. In the first part, time-resolved imaging is used to investigate the mechanisms responsible for the laser-induced ejection of ink. Fluid ejections driven by a rapidly expanding gas cavity within the ink film are observed and analyzed within the context of similar work on cavitation bubble formation, revealing that the unique geometry and size scale of LIFT invokes novel flow behavior. An alternative mechanism is also observed in which the fluid is ejected by the rapid formation of blister on a polymer layer adjacent to the ink film. The dynamics of the blister expansion and associated ink ejection are analyzed as a function of system properties and processing parameters. In the second part, a computational model of the blister-actuated ejection process is developed and used to study the novel regime of free-surface jetting from thin liquid films. The model is first validated against experimental results. It is then used to develop a fundamental understanding of the ejection process as well as conduct a detailed parametric study on the influence of system parameters on printing performance. These results help to uncover some of the fundamental limitations of the LIFT process as well as provide means by to push these limits.

Brown, Matthew S.

308

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

SciTech Connect

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

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

2011-04-01

309

Simulation and characterization of laser induced deformation processes  

NASA Astrophysics Data System (ADS)

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

Fan, Yajun

310

Superfluid {sup 4}He Quantum Interference Grating  

SciTech Connect

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

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

2008-08-22

311

Blazed phononic crystal grating  

NASA Astrophysics Data System (ADS)

It is well known that blazed optical diffraction gratings can significantly increase the diffraction efficiency of plane waves for a selected angle of incidence. We show that by combining blazing with a phononic band gap, diffraction efficiency approaching 100% can be achieved for acoustic waves. We obtain experimentally 98% diffraction efficiency with a two-dimensional phononic crystal of rotated steel rods of square cross-section immersed in water. This result opens the way toward the design of efficient phononic crystal gratings.

Moiseyenko, Rayisa P.; Liu, Jingfei; Declercq, Nico F.; Laude, Vincent

2013-01-01

312

Cryogenic infrared grating spectrometer.  

PubMed

A liquid-helium-cooled Ebert-Fastie grating spectrometer for use in a sounding rocket is described. Twelve detectors and associated filters separate the 5-70-microm spectral range into twelve intervals, each of which is scanned as the grating is rotated. The instrument was launched into an aurora from Fort Churchill, Canada, but a cryogenic failure occurred early in the flight, and only a small amount of data was obtained. PMID:20154781

McNutt, D P; Shivanandan, K; Daehler, M; Feldman, P D

1975-05-01

313

Cryogenic infrared grating spectrometer  

Microsoft Academic Search

A liquid-helium-cooled Ebert-Fastie grating spectrometer for use in a sounding rocket is described. Twelve detectors and associated filters separate the 5-70-micrometer spectral range into twelve intervals, each of which is scanned as the grating is rotated. The instrument was launched into an aurora from Fort Churchill, Canada, but a cryogenic failure occurred early in the flight, and only a small

D. P. McNutt; K. Shivanandan; M. Daehler; P. D. Feldman

1975-01-01

314

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

SciTech Connect

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

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

2011-07-15

315

Laser-induced fluorescence studies of HfF+ produced by autoionization  

NASA Astrophysics Data System (ADS)

Autoionization of Rydberg states of HfF, prepared using the optical-optical double resonance technique, holds promise to create HfF+ in a particular Zeeman level of a rovibronic state for an electron electric dipole moment search. We characterize a vibronic band of Rydberg HfF at 54 cm-1 above the lowest ionization threshold and directly probe the state of the ions formed from this vibronic band by performing laser-induced fluorescence on the ions. The Rydberg HfF molecules show a propensity to decay into only a few ion rotational states of a given parity and are found to preserve their orientation qualitatively upon autoionization. We show empirically that we can create 30% of the total ion yield in a particular |J+, M+> state and present a simplified model describing autoionization from a given Rydberg state that assumes no angular dynamics.

Loh, Huanqian; Wang, Jia; Grau, Matt; Yahn, Tyler S.; Field, Robert W.; Greene, Chris H.; Cornell, Eric A.

2011-10-01

316

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

317

Sympathetic crystallization of CaH+ produced by a laser-induced reaction  

NASA Astrophysics Data System (ADS)

We investigated sympathetic Coulomb crystallization of CaH+ ions produced by a laser-induced reaction through an excited state according to Ca40+(4p2P1/2) + H2 ? Ca40H+ + H. Ca40H+ ions stored in a linear Paul trap were characterized by their secular-motion excitation spectrum and by the modified fluorescence images of crystallized Ca+ ions. The number of two-species crystallized ions, the secular motion temperature, and the structure were determined by molecular dynamics simulations. Both the observed two-species ion crystals and simulation images demonstrate that the CaH+ ions were sympathetically crystallized with their secular-motion temperature being less than 10 mK. We determined reaction rates from fluorescence images of two-species Coulomb crystals by systematically changing the reaction time. In addition a lower limit for the reaction rate coefficient k=8×10-10 cm3/s was obtained.

Kimura, Naoki; Okada, Kunihiro; Takayanagi, Toshinobu; Wada, Michiharu; Ohtani, Shunsuke; Schuessler, Hans A.

2011-03-01

318

Laser induced ultrafast magnetization reorientation in two dimensional arrays of Fe nanoparticles  

NASA Astrophysics Data System (ADS)

We report on our recent study of ultrafast demagnetization and reorientation dynamics induced by femtosecond optical pulses in two dimensional arrays of magnetic nanoparticles. The transient Faraday rotation signal and magnetic hysteresis loops were acquired with a probe beam following excitation by pump pulses in the 50-nm Fe nanoparticle arrays. We observed rapid change and recovery of magnetization hysteresis loops of about 50 fs along with excitation of 50 fs optical pulses under Voigt geometry. The processes are consistent with the ultrafast coherent magnetic responses of the sample and clearly show that the mechanisms of optomagnetic interactions do not rely on laser-induced heating but have a nonthermal origin. Our results clearly show the feasibility of ultrafast optical control of both the magnetization and the magnetocrystalline anisotropy.

Cevher, Zehra; Gong, Yu; Lai, Wei; Ren, Yuhang; Kim, C.; Delikanli, S.; Zeng, Hao

2010-03-01

319

Systematic investigation of sustained laser-induced incandescence in carbon nanotubes  

NASA Astrophysics Data System (ADS)

A focused laser beam irradiating on aligned carbon nanotubes (CNTs) in moderate vacuum results in bright and sustained laser-induced incandescence (LII) in CNTs. The incandescence corresponds to blackbody radiation from laser-heated CNTs at ~2400 K. Post-LII craters with well-defined ring boundaries in the CNT array were observed and examined with scanning electron microscopy and Raman spectroscopy. The enhanced purity of CNTs after LII as indicated by Raman spectroscopy studies was attributed to the removal of amorphous carbons on the as-grown CNTs during LII. A dynamic study of the crater formation further elucidates the nature of such craters. Through a systematic study of the effect of vacuum level and gaseous environment on LII, we discovered the process of thermal runaway during LII in CNTs. Thermal runaway is a threat to a sustained LII and can be prevented in nitrogen and argon environments. Oxygen was found to be responsible for thermal runaway reactions.

Lim, Zhi Han; Lee, Andrielle; Lim, Kassandra Yu Yan; Zhu, Yanwu; Sow, Chorng-Haur

2010-03-01

320

Interaction and Fragmentation of Pulsed Laser Induced Microbubbles in a Narrow Gap  

NASA Astrophysics Data System (ADS)

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

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

2006-01-01

321

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

322

Bragg gratings in ORMOCERs  

NASA Astrophysics Data System (ADS)

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

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

1997-10-01

323

Laser driven grating linac  

SciTech Connect

The fields induced over a grating exposed to plane parallel light are explored. It is shown that acceleration is possible if either the particles travel skew to the grating lines, or if the radiation is falling at a skew angle onto the grating. A general theory of diffraction in this skew case is given. In one particular case numerical solutions are worked out for some deep grating. It is found that accelerating fields larger even than the initial fields can be obtained, the limit being set by resistive losses on the grating surface. Simple calculations are made to see what accelerating fields might be obtained using CO/sub 2/ lasers. Accelerations of 2 or 20 GeV per meter seem possible depending on whether the grating is allowed to be destroyed or not. Power requirements, injection and focussing are briefly discussed and no obvious difficulties are seen. It is concluded, therefore, that the proposed mechanism should be considered as a good candidate for the next generation of particle accelerators.

Palmer, R B

1980-01-01

324

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

NASA Astrophysics Data System (ADS)

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

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

2008-01-01

325

Stoichiometric changes to KH2PO4 during laser-induced breakdown  

Microsoft Academic Search

The local structure of KH2PO4 crystals (so-called KDP) at laser-induced damage sites created by irradiation with ~3-ns, 355-nm laser pulses is studied by a combination of Raman scattering and photoluminescence spectroscopies. We compare spectra from pristine material, surface and bulk laser-induced damage sites, as well as from KPO3 references. Results show that irradiation with fluences above the laser-induced breakdown threshold

Raluca A. Negres; Sergei O. Kucheyev; Paul P. DeMange; Christopher W. Carr; Stavros G. Demos

2005-01-01

326

Stoichiometric changes to KH2PO4 during laser-induced breakdown  

Microsoft Academic Search

The local structure of KHPO crystals (so-called KDP) at laser-induced damage sites created by irradiation with 3-ns, 355-nm laser pulses is studied by a combination of Raman scattering and photoluminescence spectroscopies. We compare spectra from pristine material, surface and bulk laser-induced damage sites, as well as from KPO references. Results show that irradiation with uences above the laser-induced breakdown threshold

R A Negres; S O Kucheyev; P DeMange; C W Carr; S G Demos

2004-01-01

327

Temperature Dependences of Laser-Induced Damage Resistance for Dielectric Materials  

NASA Astrophysics Data System (ADS)

We evaluated the laser-induced damage resistance of dielectric coatings at temperature from 123 K to 473 K with 1064-nm wavelength at 4-ns pulse duration. In the results, laser-induced damage resistances were improved at low temperature for dielectric coatings (single layer of SiO2 and MgF2). These results are important for understanding the laser-induced damage mechanisms.

Mikami, Katsuhiro; Motokoshi, Shinji; Fujita, Masayuki; Jitsuno, Takahisa

328

Hyperspectral Laser-induced Fluorescence Imaging for Nondestructive Assessing Soluble Solids Content of Orange  

Microsoft Academic Search

Laser-induced fluorescence imaging is a promising technique for assessing quality of fruit. This paper reports on using a\\u000a hyperspectral laser-induced fluorescence imaging technique for measurement of laser-induced fluorescence from orange for predicting\\u000a soluble solids content (SSC) of fruit. A laser (632 nm) was used as an excitation source for inducing fluorescence in oranges.\\u000a Fluorescence scattering images were acquired from ‘Nanfeng’

Muhua Liu; Luring Zhang; Enyou Guo

2007-01-01

329

Laser-induced stress transients: aqueous pores of membranes  

NASA Astrophysics Data System (ADS)

Lasers can be used to enhance the delivery of a number of molecules. The model that best fits our data is for the formation of aqueous pores. These pores are present for up to 80 seconds. Our experiments have shown that laser-induced stress transients can be utilized as a vector for intracellular delivery of molecules that may or may not normally cross the cell membrane. These two conditions have been tested with Photofrin and DNA. This technology may have applications in cell and molecular biology, cancer therapy, gene therapy, and others.

Flotte, Thomas J.; Lee, Shun; Zhang, Hong; McAuliffe, Daniel J.; Taitelbaum, Jeremy; Doukas, Apostolos G.

1996-05-01

330

Laser-induced Ni(Ti) silicide formation  

SciTech Connect

Effects of Ti alloying during laser-induced Ni silicide formation is studied. Unique triple layer microstructures were found with the presence of supercell in the NiSi{sub 2} grains formed at the interface. This supercell formation was caused by a local ordering of Ni and Si atoms that favor lower free energy during rapid solidification. Ti rapidly segregates from the alloy melt and forms a protective TiO{sub x} overlayer on the surface during solidification. Melt front progressing towards the Ni-rich region leads to quenching of an amorphous layer sandwiched between NiSi{sub 2} grains and the TiO{sub x} overlayer.

Setiawan, Y.; Lee, P.S.; Pey, K.L.; Wang, X.C.; Lim, G.C. [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore) and Chartered Semiconductor Manufacturing Ltd., 60 Woodlands Industrial Park D, Street 2, Singapore 738406 (Singapore); School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Microelectronics Center, School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Singapore Institute of Manufacturing Technology (SimTECH), 71 Nanyang Drive, Singapore 638075 (Singapore)

2006-03-13

331

Remote sensing of phytoplankton using laser-induced fluorescence  

SciTech Connect

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

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

1993-06-01

332

Laser-induced photochemistry of 4-nitroaromatic initiators of polymerization  

NASA Astrophysics Data System (ADS)

A structure-reactivity study on 4-nitro-1-naphthylamine (NNA) and N-acethyl-4-nitro-1-naphthylamine (ANNA), efficient photoinitiators of polymerization in the presence of N, N-dimethylaniline (DMA), was carried out applying time-resolved laser (337 nm) spectroscopy. The laser-induced phosphorescence of these initiators is efficiently quenched by DMA inducing the appearance of new emissions as result of radiationless processes. The spectral and temporal characteristics of these new bands together with their dependence on both the laser intensity and irradiation time allowed their assignation and provided evidence for the photosensitization process of DMA from the excited initiator to be the photoinitiation mechanism of polymerization.

Costela, A.; Garc?´a-Moreno, I.; Garc?´a, O.; Sastre, R.

2000-05-01

333

Colloid formation and laser-induced bleaching in fluorite  

SciTech Connect

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

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

2004-11-08

334

Dual beam spectrometer using laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

A laser-induced breakdown spectroscopy (LIBS) analog of a dual beam spectrometer is described and applied to the determination of trace components present in aqueous samples. It is shown that the complexity of such an instrument can be greatly reduced by using a single imaging spectrograph and two-dimensional detector to record the LIBS spectrum from the analyte and reference channels simultaneously. Implementation of the dual beam technique results in substantial spectral simplification and corresponding lower detection limits in LIBS analysis of liquids.

Yaroshchyk, Pavel; Morrison, Richard J. S.; Body, Doug; Chadwick, Bruce L.

2004-11-01

335

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

336

Quasiadiabatic approach for laser-induced single-bubble sonoluminescence.  

PubMed

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

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

2012-01-04

337

A laser-induced fluorescence diagnostic for divertors  

SciTech Connect

It is proposed that the technique of laser-induced fluorescence (LIF) be used to measure local ion velocity distributions in tokamak divertors. Recent theoretical work has indicated the existence of highly populated excited states of many partially stripped ions. These states are often connected to nearby levels by means of visible radiation, allowing useful LIF schemes to be devised. Passive spectroscopic measurements on DIII--D will be presented which verify some of the theoretical predictions. We considered ten Be-like and Mg-like ions and were able to identify over 150 LIF schemes. A possible laser system and experimental layout for the DIII--D tokamak will be presented.

McChesney, J.M.; Lippmann, S.I. (General Atomics, San Diego, California 92186-9784 (United States)); Goldstein, W.H.; Fournier, K.B. (Lawrence Livermore National Laboratory, Livermore, California 94551-9900 (United States))

1995-01-01

338

Nonresonant Referenced Laser-Induced Thermal Acoustics Thermometry in Air  

NASA Astrophysics Data System (ADS)

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

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

1999-01-01

339

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

340

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.

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

2011-01-01

341

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

342

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

343

Laser-induced fluorescence detection of stomach cancer using hypericin  

NASA Astrophysics Data System (ADS)

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

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

1996-12-01

344

Laser-induced photochemistry of nickel chelate thin films  

NASA Astrophysics Data System (ADS)

This work is devoted to the investigation of laser-induced decomposition mechanism of solid films and powders of nickel (II) chelate complexes with dimethylglyoxime Ni (DMG)2 and with dehydrogenated free-radical methyl derivative of 1,2- hydroxylaminooxime Ni(HAO)2. A comparison of stable gaseous products of laser-induced decay of these complexes with those of thermal decomposition have shown considerable difference between them. Sufficiently threshold character of the conversion degree dependence on the power density of XeCl excimer laser irradiation was revealed in the experiments. These two facts being correlated with the data on positive and negative ion chemical ionization mass spectrometry allow to propose a primary process to be predominantly photochemical with two-photon initiation mechanism. The vertical photoionization of one of chelate molecules is suggested to be accompanied by electron transfer to lattice and then by localization of excess electron on antibonding level of neighboring chelate molecule resulting in its fragmentation. The secondary processes of solid chelate decomposition are determined by the pecularities of electronic and stereochemical structure of the complexes. Thin layers of these chelates applied onto Si and SiO2 substrates decompose explosion-like in air under the influence of radiation pulse of XeCl excimer laser. A plume of decomposition products is thrown from the substrate into atmosphere, and a thin layer of dielectric film with refractive index close to the value for nickel hydroxide is deposited on the substrate.

Larionov, Stanislav V.; Badalian, Aram M.; Polyakov, Oleg V.; Prokhorova, Stalina A.; Bakhturova, Lyudmila F.; Myachina, Lyudmila I.

1994-07-01

345

Laser-induced breakdown spectroscopy of tantalum plasma  

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

346

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

2007-10-01

347

Detection of hydrogen peroxide using photofragmentation laser-induced fluorescence.  

PubMed

Photofragmentation laser-induced fluorescence (PF-LIF) is for the first time demonstrated to be a practical diagnostic tool for detection of hydrogen peroxide. Point measurements as well as two-dimensional (2D) measurements in free-flows, with nitrogen as bath gas, are reported. The present application of the PF-LIF technique involves one laser, emitting radiation of 266 nm wavelength, to dissociate hydrogen peroxide molecules into OH radicals, and another laser, emitting at 282.25 nm, to electronically excite OH, whose laser-induced fluorescence is detected. The measurement procedure is explained in detail and a suitable time separation between photolysis and excitation pulse is proposed to be on the order of a few hundred nanoseconds. With a separation time in that regime, recorded OH excitation scans were found to be thermal and the signal was close to maximum. The PF-LIF signal strength was shown to follow the same trend as the vapor pressure corresponding to the hydrogen peroxide liquid concentration. Thus, the PF-LIF signal appeared to increase linearly with hydrogen peroxide vapor-phase concentration. For 2D single shot measurements, a conservatively estimated value of the detection limit is 30 ppm. Experiments verified that for averaged point measurements the detection limit was well below 30 ppm. PMID:18230210

Johansson, O; Bood, J; Aldén, M; Lindblad, U

2008-01-01

348

Direct probing of chromatography columns by laser-induced fluorescence  

NASA Astrophysics Data System (ADS)

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

McGuffin, V. L.

1992-12-01

349

Laser-induced bubble formation in the retina  

NASA Astrophysics Data System (ADS)

Bubble formation in the retinal pigment epithelium by submicrosecond laser pulses may be a source of laser induced retinal damage. Heat conduction away from absorbing melanin granules requires timescales on the order of microseconds. For pulses of shorter duration, all energy absorbed is effectively absorbed as a (delta) -function in time, and energy concentration may be high enough to cause vaporization of the surrounding medium. This occurs at lower fluences than required for thermal denaturation of a significant volume of cellular material. The adiabatic nature of the absorption and subsequent expansion is used to develop expressions for the calculation of maximum bubble size as a function of laser intensity and melanosome properties such as radius and absorption coefficients. We describe the analysis that went into the development of the bubble size expression and also present the results for representative calculations of maximum bubble radius. We find that our expression leads to a threshold for the formation of bubbles in the retinal pigment epithelium that is close to the ED50 experimentally measured for laser induced retinal damage.

Gerstman, Bernard S.; Thompson, Charles R.; Jacques, Steven L.; Rogers, Mark E.

1995-05-01

350

Laser-induced nuclear magnetic resonance splitting in hydrocarbons  

NASA Astrophysics Data System (ADS)

Irradiation of matter with circularly polarized light (CPL) shifts all nuclear magnetic resonance (NMR) lines. The phenomenon arises from the second-order interaction of the electron cloud with the optical field, combined with the orbital hyperfine interaction. The shift occurs in opposite directions for right and left CPL, and rapid switching between them will split the resonance lines into two. We present ab initio and density functional theory predictions of laser-induced NMR splittings for hydrocarbon systems with different sizes: ethene, benzene, coronene, fullerene, and circumcoronene. Due to the computationally challenging nature of the effect, traditional basis sets could not be used for the larger systems. A novel method for generating basis sets, mathematical completeness optimization, was employed. As expected, the magnitude of the spectral splitting increases with the laser beam frequency and polarizability of the system. Massive amplification of the effect is also observed close to the optical excitation energies. A much larger laser-induced splitting is found for the largest of the present molecules than for the previously investigated noble gas atoms or small molecules. The laser intensity required for experimental detection of the effect is discussed.

Ikäläinen, Suvi; Lantto, Perttu; Manninen, Pekka; Vaara, Juha

2008-09-01

351

Vertical angular selectivity and grating degeneracy of volume holographic gratings  

Microsoft Academic Search

The vertical angular selectivity of volume holographic gratings in photorefractive crystals is investigated both theoretically and experimentally. The vertical selective angle and the shape of the grating degeneracy lines are derived by using a simplified geometrical model relating the k-vector sphere to the reference point plane. The study shows that volume gratings have finite selectivity in vertical direction, so that

Quan Yuan; Shiquan Tao; Zuqing Jiang; Xinchang Yang

1996-01-01

352

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

SciTech Connect

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

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

2009-05-01

353

Dipole radiation into grating structures  

Microsoft Academic Search

We present a detailed electromagnetic analysis for the radiation of an electric source located inside grating structures. Our analysis is based on the differential method and uses the scattering-matrix algorithm. We show that gratings that exhibit periodic modulations along two spatial directions (crossed gratings) enable one to couple out the totality of the light emitted by the source into the

Hervé Rigneault; Fabien Lemarchand; Anne Sentenac

2000-01-01

354

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

Microsoft Academic Search

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

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

2008-01-01

355

Anomalous laser induced bunch lengthening on the ACO storage ring free electron laser  

Microsoft Academic Search

Laser induced bunch lengthening has been measured on the ACO Storage Ring Free Electron Laser (SRFEL) in the anomalous bunch lengthening regime. The experimental results show correlations between the appearance of coherent modes in the electron bunch and anomalous behavior in the presence of the laser. Simultaneous time resolved laser induced bunch lengthening, mode strength, bunch length, and synchrotron sideband

K. E. Robinson; J. M. J. Madey; M. F. Velghe; D. A. G. Deacon

1983-01-01

356

Anomalous laser induced bunch lengthening on the ACO Storage Ring Free Electron Laser. Interim report  

Microsoft Academic Search

Laser induced bunch lengthening has been measured on the ACO Storage Ring Free Electron Laser (SRFEL) in the anomalous bunch lengthening regime. The experimental results show correlations between the appearance of coherent modes in the electron bunch and anomalous behavior in the presence of the laser. Simultaneous time resolved laser induced bunch lengthening, mode strength, bunch length, and synchrotron sideband

K. E. Robinson; J. M. J. Madey; M. F. Velghe; D. A. G. Deacon

1983-01-01

357

Laser Induced Breakdown Spectroscopy: An Approach to Detect Adulteration in Turmeric  

Microsoft Academic Search

In the present paper, four turmeric samples A, B, C and D were analyzed using the laser induced breakdown spectroscopic technique. Laser induced breakdown spectra of A, B, and C give the spectral lines of elements such as carbon (C), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), iron (Fe) and molecular bands of CN, whereas spectral signatures of toxic

Manju Tiwari; Rahul Agrawal; Ashok Kumar Pathak; Awadhesh Kumar Rai; Gyanendra Kumar Rai

2012-01-01

358

Optical Measurement of a Laser Induced Micro Shock Wave on a Metal Surface  

Microsoft Academic Search

Laser induced streaming is one of the interesting phenomena. When we provide a highly concentrated energy in a small region with laser beam, an induced streaming, such as micro shock wave or laser induced thermal acoustics is observed in the region. In the present paper, a micro shock wave in air which was induced by laser irradiation was observed by

Hiroyuki Hirahara; Masaru Fujinami; Masaaki Kawahashi

2008-01-01

359

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

Microsoft Academic Search

We report the experimental results of impurity contamination and laser-induced damage investigations on rapidly grown potassium dihydrogen phosphate (KDP) crystals. Using absorption spectroscopy and chemical analysis, we determined the impurity distribution in the different growing sectors of KDP single crystals. The level of impurity was dependent on starting materials and growth rate. We also studied influence of impurities on laser-induced

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

1997-01-01

360

Laser ablation laser induced fluorescence for sensitive detection of heavy metals in water  

Microsoft Academic Search

Laser Induced Breakdown Spectroscopy LIBS is a fast non-contact technique for the analysis of the elemental composition using spectral information of the emission from a laser-induced plasma. For the LIBS studies in this thesis the focus has been in using very low energy, microjoule pulses in order to give high spatial resolution and minimize the laser system requirements. This is

Yogesh Godwal

2010-01-01

361

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

Microsoft Academic Search

A nondestructive laser-induced breakdown detection technique is developed, which entails measuring the deflection of a probe laser beam due to a shock wave generated by a laser-induced breakdown of colloidal nanoparticles in liquids. Comparing this optical method with a previously developed acoustic detection method using a piezoelectric transducer, it enables remote measurement and therefore facilitates the in situ measurement of

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

2008-01-01

362

Laser Induced Nuclear Fusion, LINF, In Muonic Molecules With Ultrashort Super Intense Laser Fields  

NASA Astrophysics Data System (ADS)

Muonium molecules where muons replace electrons increase the stability of molecules to ionization at superhigh intensities, I>1020 W/cm2. We show furthermore from numerical simulations that in the nonsymmetric series, pdu, dtu, ptu, the permanent dipole moments can be used to enhance LINF, Laser Induced Nuclear Fusion by laser induced recollision of the light nucleus with the heavier nucleus.

Bandrauk, Andre D.; Paramonov, Gennady K.

2010-02-01

363

Radial Variation of Refractive Index, Plasma Frequency and Phase Velocity in Laser Induced Air Plasma  

Microsoft Academic Search

Laser-induced breakdown spectroscopy (LIBS) is a nonintrusive technique that needs no sample preparation and even recently, quantitative measurements were done without the need for calibration standards. Much research has been done on the laser induced air plasma to study the spatial variation of plasma parameters in the axial direction of the laser beam. In this paper, we report investigation on

Manny Mathuthu; Rita M. Raseleka; Andrew Forbes; Nicholas West

2006-01-01

364

Gain-grating analysis of a self-starting self-pumped phase-conjugate Nd:YAG loop resonator  

Microsoft Academic Search

We investigate both experimentally and theoretically the contribution of the different gain gratings in a self-starting self-pumped phase-conjugate Nd:YAG loop resonator. Thanks to a transient model, we show that the transmission-grating configuration is more efficient than the reflection-grating configuration, and that their temporal dynamics are different, in agreement with the experiment. Maximum extraction is obtained for the four-grating configuration. The

Pierre Sillard; Arnaud Brignon; Jean-Pierre Huignard

1998-01-01

365

A laser microvibration transducer based on two diffraction gratings  

Microsoft Academic Search

A laser microvibrations transducer based on diffraction of a laser beam on a system of two diffraction gratings is described. The transducer has an experimental threshold of detection of 0.3A°, a dynamic range of about 10 mum. It contains no expensive elements (simple glass stepped gratings) and it is easy to implement and align. Furthermore it is self-calibrating. It can

Alphonse Niyibizi

2004-01-01

366

Application of moving gratings in BSO to optical pattern recognition  

NASA Astrophysics Data System (ADS)

Moving grating technique is applied to dynamic holographic recording to overcome the difficulties of the fluctuation of the diffraction efficiency and the funning effect in photorefractive crystal BSO. Various nonlinear effects caused by moving gratings at large fringe modulations are experimentally investigated. It is shown in the application of optical pattern recognition that the probability of an error detection is reduced and the signal-to-noise ratio is considerably enhanced. Experimental results are presented.

Mu, Guoguang; Wang, Zhao-Qi

1996-10-01

367

Compatibility design for time grating interface based on forecasting method  

NASA Astrophysics Data System (ADS)

Time grating is a novel displacement sensor which employs time to measure space. A new predictive method for predicting the dynamic angular displacement of CNC rotary table is presented with time series. In addition, feedback interface for rotary transformer is designed to update data speed for time grating in the measurement process. Experiment results prove that forecast error for acceleration range from -0.00026"/ms2 to 0.00028"/ms2, and forecast angular displacement error is within +/-2".

Zheng, Fangyan; Chen, Ziran; Lu, Jin; Dong, Chun

2011-08-01

368

Liquid film characterization in horizontal, annular, two-phase, gas–liquid flow using time-resolved laser-induced fluorescence  

Microsoft Academic Search

A non-intrusive optical technique was developed to provide time-resolved longitudinal and cross-sectional images of the liquid\\u000a film in horizontal annular pipe flow of air and water, revealing the interfacial wave behavior. Quantitative information on\\u000a the liquid film dynamics was extracted from the time-resolved images. The planar laser-induced fluorescence technique was\\u000a utilized to allow for optical separation of the light emitted

P. S. C. Farias; F. J. W. A. Martins; L. E. B. Sampaio; R. Serfaty; L. F. A. Azevedo

369

Laser-Induced Fluorescence Detection in High-Throughput Screening of Heterogeneous Catalysts and Single Cells Analysis.  

National Technical Information Service (NTIS)

Laser-induced fluorescence detection is one of the most sensitive detection techniques and it has found enormous applications in various areas. The purpose of this research was to develop detection approaches based on laser-induced fluorescence detection ...

H. Su

2001-01-01

370

Laser ablation laser induced fluorescence for sensitive detection of heavy metals in water  

NASA Astrophysics Data System (ADS)

Laser Induced Breakdown Spectroscopy LIBS is a fast non-contact technique for the analysis of the elemental composition using spectral information of the emission from a laser-induced plasma. For the LIBS studies in this thesis the focus has been in using very low energy, microjoule pulses in order to give high spatial resolution and minimize the laser system requirements. This is a regime that we refer to as microLIBS. Under such conditions it is important to maximize the signal detected to give the lowest limit of detection LOD possible. One technique to improve the signal to noise ratios is by coupling LIBS with Laser Induced Fluorescence. This is a technique where the first pulse creates a vapor plume and the second pulse tuned to a resonant absorption line of the species of interest re-excites the plume. We term this technique as Laser ablation Laser Induced Fluorescence LA-LIF. We have been investigating the performance of LA-LIF at low pulse energies (? 1 mJ for both pulses) for the detection of elemental contaminants in water. This technique allows reasonable performance compared to high energy single-pulse LIBS, but at a much reduced total energy expenditure. This allows LODs in the parts per billion range ppb range which typically cannot be obtained with low energy single pulse probing of the systems. This approach or exceeds the sensitivities which can be obtained with many shots using much larger energy systems. In this thesis we investigated the performance of LIBS at low pulse energies for the detection of Pb as a contaminant in water. An LOD of 70 ppb was obtained for an accumulation of 100 shots with the ablation laser pulse energy of 250 muJ and an excitation laser pulse energy of 8 muJ. A systematic study of the detector conditions was made for the system for the detection of Pb. Scaling laws for the LOD in terms of the pump and probe energies were measured and also the effect of detector gain, the gate delay and the gate width were studied. In this thesis LIBS and LA-LIF were also used to analyze ultralow volumes of analyte in liquids in micro uidic geometries. LIBS was applied for the detection of Na in liquid droplets in a microfluidic system. The detection of Na as low as 360 femtograms was demonstrated for 100 shots integrated in this system. An LOD of 7 ppm for Pb for 100 shot accumulation was demonstrated using the LA-LIF technique on an 18 mum diameter microdroplet. To study the laser interaction with the water targets the MEDUSA one dimensional hydrocode was used. The propagation of the shockwave and plume dynamics were studied using this modeling code. The expansion of the plume was studied and compared to experimentally measured values and to physical models for blast wave expansion and stagnation. Two preconcentration techniques were also studied, one of which used a wood-chip as a substrate to absorb the analyte liquid and wick the salt on to the surface for analysis and the other used an electroplating technique to plate the analyte metal as a thin film on a substrate metal used as a cathode. The electroplating method for preconcentration was also studied using a microchip laser and a LOD of 6.4 ppb for Pb in water was obtained for an accumalation of 200,000 shots.

Godwal, Yogesh

371

Minimizing contamination to multilayer dielectric diffraction gratings within a large vacuum system  

NASA Astrophysics Data System (ADS)

The University of Rochester's Laboratory for Laser Energetics (LLE) has recently completed the construction of the OMEGA EP short-pulse, petawatt laser system. A major structure for OMEGA EP is the grating compressor chamber (GCC). This large (15,750-ft3) vacuum chamber contains numerous optics used in laser-pulse compression of two 40-cm-sq-aperture, IR (1054-nm) laser beams. Critical to this compression, within the GCC, are eight sets (four per beamline) of tiled (e.g., three optical elements precisely held side by side to act as one element) multilayer-dielectric (MLD)-diffraction-grating assemblies (three gratings per assembly) that provide the capability for producing 2.6-kJ output IR energy per beam at 10 ps. The primary requirements for each of the 24 large-aperture (43-cm × 47-cm) gratings are a high diffraction efficiency greater than 95%, a peak-to-valley wavefront quality of less than ?/4 waves at 1054 nm, and a laser-induced-damage threshold greater than 2.7 J/cm2 at 10-ps pulse width (measured at normal beam incidence). Degradation of grating laser-damage thresholds due to adsorption of contaminants must be prevented to maintain system performance.

Ashe, B.; Marshall, K. L.; Mastrosimone, D.; McAtee, C.

2008-08-01

372

Optical grating coupler biosensors  

Microsoft Academic Search

By incorporating a grating in a planar optical waveguide one creates a device with which the spectrum of guided lightmodes can be measured. When the surface of the waveguide is exposed to different solutions, the peaks in the spectrum shift due to molecular interactions with the surface. Optical waveguide lightmode spectroscopy (OWLS) is a highly sensitive technique that is capable

J Vörös; J. J Ramsden; G Csúcs; I Szendr?; S. M De Paul; M Textor; N. D Spencer

2002-01-01

373

Resonantly Enhanced Grating Coupler.  

National Technical Information Service (NTIS)

An apparatus and method for increasing efficiency of grating couplers are disclosed. The apparatus through the use of a defect or a reflective element allows coupling of light around a normal or nearly normal angle with a high efficiency. The method discl...

A. Scherer J. Witzens

2005-01-01

374

Cryogenic Grating Spectrometer.  

National Technical Information Service (NTIS)

The Cryogenic Grating Spectrometer (CGS) first flew on the KAO in 1982 December and has been open to guest investigators since 1984 October. In the past 12 years it has completed over 100 research flights supporting 13 different principal investigators st...

E. F. Erickson M. R. Haas S. W. J. Colgan J. P. Simpson R. H. Rubin

1995-01-01

375

Electro-optical tunable waveguide Bragg gratings in lithium niobate induced by femtosecond laser writing.  

PubMed

We report the fabrication of femtosecond laser-induced, first-order waveguide Bragg gratings in lithium niobate in the low repetition rate regime. Type-II waveguides are written into an x-cut lithium niobate wafer and structured periodically to achieve narrowband reflections at wavelengths around 1550 nm. Additionally, electrodes are employed to allow for electro-optic tuning of the spectral response. We demonstrate wavelength control of the central reflection peak by applying a static external electric field. A maximum shift of the reflection peak of ?? = 625 pm is observed. PMID:23187546

Horn, W; Kroesen, S; Herrmann, J; Imbrock, J; Denz, C

2012-11-19

376

Femtosecond-laser-induced breakdown spectroscopy of explosives  

NASA Astrophysics Data System (ADS)

We use femtosecond laser-induced breakdown spectroscopy (LIBS) to detect trace amounts of TNT and RDX. A high-power pulsed laser is used in LIBS to form a plasma on the material surface and the optical emission from the plasma is spectrally analyzed to determine the material composition. Femtosecond LIBS results for TNT and RDX on aluminum substrates and glass slides are reported. Results are examined in terms of the optical properties of the substrate and the strong linear absorption for aluminum is contrasted with the weaker multiphoton absorption for glass. Optical microscope images of the ablated explosives are shown for femtosecond and nanosecond laser excitation. Fragmentation studies by femtosecond laser mass spectrometry are used to interpret LIBS results.

Dikmelik, Yamac; McEnnis, Caroline; Spicer, James B.

2006-06-01

377

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.

TEXTOR Team 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.

2013-07-01

378

Simulation of infrared picosecond laser-induced electron emissionfrom semiconductors  

SciTech Connect

In this study, we present a self-consistent model forpicosecond laser induced electron emission from silicon. Surface electronemission due to a pulsed laser excitation originates from thermionic andphotoelectric effects, both of which depend on the surface electrontemperature and incident laser pulse intensity. By numerically solving aset of coupled transport equations, time dependent surface electrontemperature as well as lattice temperature was determined. The electronemission rates and electron yields due to photoelectric and thermioniceffects have been studied for varying pulse width and pulse intensity.For picosecond pulses at 1064 nm, the dominant emission mechanism wasfound to be photoelectric emission for pulse fluences below the meltingthreshold. In addition, a comparison between electron emission due to thepicosecond infrared pulse and a picosecond 532 nm pulse was alsopresented.

Mao, Samuel S.; Mao, Xiang-Lei; Greif, Ralph; Russo, Richard E.

1997-07-01

379

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

380

Refining femtosecond laser induced periodical surface structures with liquid assist  

NASA Astrophysics Data System (ADS)

Laser induced periodic surface structures were generated on silicon wafer using femtosecond laser. The medium used in this study is both air and ethanol. The laser process parameters such as wavelength, number of pulse, laser fluence were kept constant for both the mediums. The focus of the study is to analyze spatial wavelength. When generating surface structures with air as a medium and same process parameter of the laser, spatial wavelength results showed a 30% increase compared to ethanol. The cleanliness of the surface generated using ethanol showed considerably less debris than in air. The results observed from the above investigation showed that the medium plays a predominant role in the generation of surface structures.

Jiao, L. S.; Ng, E. Y. K.; Zheng, H. Y.

2013-01-01

381

Radioactive contamination screening with laser-induced fluorescence  

SciTech Connect

The ability to induce, detect and discriminate fluorescence of uranium oxides makes available new capabilities for screening the surface of large complex facilities for uranium. This paper will present the results of field tests evaluate laser-induced fluorescence (LIF) as a contamination screening tool and report on the progress to produce a field portable instrument for uranium surveys on exposed surfaces. The principal effect is to illuminate the surface of an object or an area with a remotely-located light source, and to evaluate the re-radiated emission energy. A gated intensified CCD camera was used with ultraviolet (UV) laser excitation to discriminate the phosphorescent (persistent) green uranium emission from the prompt background fluorescence which results from excitation of plants, concrete, soils, and other background materials.

Sheely, R. [Oak Ridge K-25 Site, TN (United States); Di Benedetto, J. [EG and G Energy Measurements, Inc., Goleta, CA (United States). Santa Barbara Operations

1994-06-01

382

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

383

Particulate measurement issues in diesel exhausts using laser induced incandescence  

SciTech Connect

A number of studies in the recent past have identified Laser Induced Incandescence (LII) as a versatile technique for in-flame measurement of soot concentrations. Recently, a number of researchers have focused their attention in adapting this technique to measure particulate in diesel exhausts. However the agreement with established physical sampling techniques, such as the EPA recommended filter paper collection method, was found to be less than ideal. This paper reports the efforts to adapt this technique for diesel exhaust characterization. Many of the factors affecting LII signal were identified through computer modeling. Parameters that could not be determined through such a model were determined experimentally following a parametric study. Subsequently, LII measurements were performed in the exhaust of a modified lab burner, with conditions close to that of diesel engine exhausts. Such measurements show excellent agreement with those performed using the standard filter paper collection technique.

Gupta, S. B.; Poola, R. B.; Sekar, R.

2000-07-03

384

Nanoscale Cr Deposition by Laser-Induced Forward Transfer  

NASA Astrophysics Data System (ADS)

Laser-Induced Forward Transfer (LIFT) is a direct-write addition technique used in creating, modifying and fixing microscale devices. We study the transfer energy thresholds, ablation thresholds and transfer spot sizes of continuous (of 80, 60, 40, and 20 nm thickness) and patterned (of 80 nm thickness; 85 and 270 nm diameter) Cr films. As the film thickness decreases, the energy thresholds decrease; as well as the average diameter of the transfer spots. The continuous films (from 80 to 20 nm thickness) produced circular and reproducible transfer spots with diameters from ˜420 to ˜85 nm at transfer thresholds from ˜250 to ˜120 mJ/cm^2, respectively. Dot-patterned films delivered somewhat smaller spot sizes (down to ˜70 nm) at surprisingly lower laser flux (i.e., <1/4). This suggests that different physical effects dominate in each case, and its understanding will enable us to create more efficient and versatile nanoscale deposition methods.

Sametoglu, Vahit; Sauer, Vincent; Tsui, Ying

2012-02-01

385

Microdroplet deposition by laser-induced forward transfer  

NASA Astrophysics Data System (ADS)

Laser-induced forward transfer was used to deposit aluminum and nickel microdroplets onto a substrate using a Q-switched neodymium:Yttrium-aluminum-garnet laser. The droplets have diameters of a few microns, much smaller than the laser spot diameter, and are transferred at fluences slightly above the melting threshold. Scanning electron microscopy shows that the original donor film is deformed after laser irradiation, such that the film protrudes outward from the center of the laser spot. The film expands during laser heating, but is constrained until the melt interface reaches the free surface. When this occurs, the film is no longer constrained, allowing the melt to rapidly expand, forming the protrusions from which droplets are ejected.

Willis, David A.; Grosu, Vicentiu

2005-06-01

386

Laser-induced photo-thermal magnetic imaging  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

387

Characterization of laser - induced plasmas by atomic emission spectroscopy  

NASA Astrophysics Data System (ADS)

In this work, Laser-induced breakdown spectroscopy (LIBS) has been applied to characterization of plasmas generated in air at atmospheric pressure from a calcium hydroxide sample with a known concentration of Mg by using an infrared Nd:YAG laser. The influence of laser irradiance on plasma morphology and emission intensity was studied. Spatially-integrated intensities of Mg I-II lines along the line-of-sight were measured for different laser energies and delay times. The plasma temperature and the electron density were determined in each case by using and algorithm that calculates the optical thickness of the spectral lines and reproduces their experimental profiles in a framework of an homogeneous plasma in LTE that takes into account the effects of self-absorption. The results obtained showed the usefulness of this approach to provide additional information retrieved from the optical thickness of spectral lines for plasma characterization in LIBS experiments.

Díaz Pace, Diego M.; Bertuccelli, Graciela; D'Angelo, Cristian A.

2011-01-01

388

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

389

Luminescence Spectra of Laser-induced Cavitation Bubbles  

NASA Astrophysics Data System (ADS)

The luminescence spectra of laser-induced cavitation bubbles near rigid boundaries are measured for various relative distances between the bubble and the boundaries. We find that the luminescence spectra of bubbles collapsing near a single boundary consist of only a blackbody continuum. Luminescence from bubbles collapsing between two parallel rigid boundaries also contains OH* emission bands similar to those found in multi-bubble sonoluminescence. In both cases, the bubble interior temperature deduced from blackbody fits decreases with the distance between bubble and boundary. The shape instabilities of the collapse near a boundary and the consequent presence of high-velocity jets inside the bubble at its minimum volume will be discussed in connection with the generation of the OH* radicals.

Brujan, Emil A.

2005-03-01

390

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

391

Noninvasive thermography of laser-induced hyperthermia using magnetic resonance  

NASA Astrophysics Data System (ADS)

The possibility to induce selective hyperthermia in a target tissue or organ is of great interest for the treatment of cancer and other diseases. An emerging application of thermotherapy is for choroidal neovascularization, a complication of age-related macular degeneration. The therapy is currently limited because the temperature required for optimal tissue response is unknown. We report here an investigation of near infrared laser-induced heating in an ocular phantom. Magnetic resonance thermography (MRT) was used as a non-invasive method to determine the temperature distribution inside the phantom during exposure to a continuous wave diode laser at 806 nm wavelength with 1 watt maximum output. The laser beam had a quasi-gaussian profile, with a radius of 0.8-2.4 mm at target. High quality temperature images were obtained from temperature-dependent phase shifts in the proton resonance frequency with a resolution of 1deg C or better, using a 2T magnet. A phantom with a layer of bovine RPE melanin of 1.5 mm thickness was used to determine the spatial resolution of the MRT measurements. Three dimensional temperature maps were also constructed showing a spatial resolution of 0.25 mm in all direction. The heat distribution depended on the laser parameters, as well as the orientation of the melanin layer with respect to the incident laser beam. The temperature profiles determined by MRT closely followed predictions of a heat diffusion model, based on the optical properties of infrared light in melanin. These results support the use of MRT to optimize laser-induced hyperthermia in a small organ such as the eye.

Maswadi, Saher M.; Glickman, Randolph D.; Dodd, Stephen J.; Gao, Jia Hong

2004-07-01

392

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

393

Binary gratings with random heights  

SciTech Connect

We analyze the far-field intensity distribution of binary phase gratings whose strips present certain randomness in their height. A statistical analysis based on the mutual coherence function is done in the plane just after the grating. Then, the mutual coherence function is propagated to the far field and the intensity distribution is obtained. Generally, the intensity of the diffraction orders decreases in comparison to that of the ideal perfect grating. Several important limit cases, such as low- and high-randomness perturbed gratings, are analyzed. In the high-randomness limit, the phase grating is equivalent to an amplitude grating plus a ''halo.'' Although these structures are not purely periodic, they behave approximately as a diffraction grating.

Rico-Garcia, Jose Maria; Sanchez-Brea, Luis Miguel

2009-06-01

394

Design and fabrication of an active polynomial grating for soft-X-ray monochromators and spectrometers  

Microsoft Academic Search

An active polynomial grating has been designed for use in synchrotron radiation soft-X-ray monochromators and spectrometers. The grating can be dynamically adjusted to obtain the third-order-polynomial surface needed to eliminate the defocus and coma aberrations at any photon energy. Ray-tracing results confirm that a monochromator or spectrometer based on this active grating has nearly no aberration limit to the overall

S.-J. Chen; C. T. Chen; S. Y. Perng; C. K. Kuan; T. C. Tseng; D. J. Wang

2001-01-01

395

Laser-induced-fluorescence studies of fragment ions: CH/sup +/ and CD/sup +/  

SciTech Connect

The dynamics of ion-molecule interactions within a mass selective rf quadrupole ion trap are studied for several ion-molecule systems. Laser induced fluorescence is used as a probe of the internal energy distributions of molecular ions under collision free conditions and under controlled collision conditions. The effects of collisions at near thermal energies (0.3 to 0.5 eV) are easily understood in terms of processes such as charge transfer and other energy transfer mechanisms. The A/sup 1/PI - X/sup 1/..sigma../sup +/ system of CH/sup +/ and CD/sup +/ has been examined under collision free conditions. The ions were produced from methane through electron impact ionization/dissociation. The observed energy distributions reflect the dynamical partitioning of dissociation exothermicity, excepting short lived electronic states. Many new transitions belonging to this electronic system have been observed and a reliable vibrational frequency for the X/sup 1/..sigma../sup +/ state has been obtained. The radiative lifetimes of CH/sup +/ and CD/sup +/ A/sup 1/PI(v = 0) states have been measured and a revised oscillator strength for the A-X transition has been derived from this data.

O'Keefe, A.

1981-08-01

396

Detection of zinc and lead in water using evaporative preconcentration and single-particle laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

A novel laser-induced breakdown spectroscopy (LIBS)-based measurement method for metals in water is demonstrated. In the presented technology a small amount of sodium chloride is dissolved in the sample solution before spraying the sample into a tubular oven. After water removal monodisperse dry NaCl aerosol particles are formed where trace metals are present as additives. A single-particle LIBS analysis is then triggered with a scattering based particle detection system. Benefits are the highly increased metal concentration in the LIBS focal volume and the static NaCl-matrix which can be exploited in the signal processing procedure. Emitted light from the emerged plasma plume is collected with wide angle optics and dispersed with a grating spectrometer. In an aqueous solution, the respective limits of detection for zinc and lead were 0.3 ppm and 0.1 ppm using a relatively low 14 mJ laser pulse energy. Zn/Na peak intensity ratio calibration curve for zinc concentration was also determined and LIBS signal dependence on laser pulse energy was investigated.

Järvinen, Samu T.; Saarela, Jaakko; Toivonen, Juha

2013-08-01

397

Line Selection and Parameter Optimization for Trace Analysis of Uranium in Glass Matrices by Laser-Induced Breakdown Spectroscopy (LIBS).  

PubMed

Laser-induced breakdown spectroscopy (LIBS) has been evaluated for the determination of uranium in real-world samples such as uraninite. NIST Standard Reference Materials were used to evaluate the spectral interferences on detection of uranium. The study addresses the detection limit of LIBS for several uranium lines and their relationship to non-uranium lines, with emphasis on spectral interferences. The data are discussed in the context of optimizing the choice of emission lines for both qualitative and quantitative analyses from a complex spectrum of uranium in the presence of other elements. Temporally resolved spectral emission intensities, line width, and line shifts were characterized to demonstrate the parameter influence on these measurements. The measured uranium line width demonstrates that LIBS acquired with moderately high spectral resolution (e.g., by a 1.25 m spectrometer with a 2400 grooves/mm grating) can be utilized for isotope shift measurements in air at atmospheric pressure with single to tens of parts per million (ppm) level detection limits, as long as an appropriate transition is chosen for analysis. PMID:24160879

Choi, Inhee; Chan, George C-Y; Mao, Xianglei; Perry, Dale L; Russo, Richard E

2013-11-01

398

A Laser Induced Breakdown Spectroscopy application based on Local Thermodynamic Equilibrium assumption for the elemental analysis of alexandrite gemstone and copper-based alloys  

NASA Astrophysics Data System (ADS)

Laser Induced Breakdown Spectroscopy (LIBS) is an appealing technique to study laser-induced plasmas (LIPs), both from the basic diagnostics point of view and for analytical applications. LIPs are complex dynamic systems, expanding at supersonic velocities and undergoing a transition between different plasma regimes. If the Local Thermodynamic Equilibrium (LTE) condition is valid for such plasmas, several analytical methods can be employed and fast quantitative analyses can be performed on a variety of samples. In the present paper, a discussion about LTE is carried out and an innovative application to the analysis of the alexandrite gemstone is presented. In addition, a study about the influence of plasma parameters on the performance of LTE-based methods is reported for bronze and brass targets.

De Giacomo, A.; Dell'Aglio, M.; Gaudiuso, R.; Santagata, A.; Senesi, G. S.; Rossi, M.; Ghiara, M. R.; Capitelli, F.; De Pascale, O.

2012-04-01

399

Laser induced damage of fused silica polished optics due to a droplet forming organic contaminant  

SciTech Connect

We report on the effect of organic molecular contamination on single shot laser induced damage density at the wavelength of 351 nm, with a 3 ns pulse length. Specific contamination experiments were made with dioctylphthalate (DOP) in liquid or gaseous phase, on the surface of fused silica polished samples, bare or solgel coated. Systematic laser induced damage was observed only in the case of liquid phase contamination. Different chemical and morphological characterization methods were used to identify and understand the damage process. We demonstrate that the contaminant morphology, rather than its physicochemical nature, can be responsible for the decrease of laser induced damage threshold of optics.

Bien-Aime, Karell; Neauport, Jerome; Tovena-Pecault, Isabelle; Fargin, Evelyne; Labrugere, Christine; Belin, Colette; Couzi, Michel

2009-04-20

400

Laser-induced jet formation and droplet ejection from thin metal films  

NASA Astrophysics Data System (ADS)

An experimental study of femtosecond laser-induced jet formation and droplet ejection from thin metal films is presented. These processes are compared to liquid jet formation during laser-induced forward transfer of viscous liquids. As a result of this comparison, a mechanism explaining the main features of laser processing of thin metal films is proposed. According to this mechanism, laser-induced generation of a molten bump and its collapse are similar to the collapse of cavitation bubbles on a liquid-air interface. Material criteria required for realization of the jetting process are discussed and supported by experimental observations.

Kuznetsov, Arseniy I.; Unger, Claudia; Koch, Jürgen; Chichkov, Boris N.

2012-03-01

401

Development of ultrasound technique to detect and characterize laser-induced microbubbles  

NASA Astrophysics Data System (ADS)

An ultrasound-based method to detect and characterize the laser-induced microbubbles was developed. This method is based on temporal measurement of passive acoustic emission from cavity during laser-tissue interaction and simultaneous active pulse-echo ultrasound probing of the cavitation bubble. These measurements were used to estimate the location of the nanosecond laser induced cavity and to monitor the spatial and temporal behavior of the microbubble. The measurements agreed with estimates derived from a well-known Rayleigh model of the cavity collapse. Overall, the studies indicate that the developed ultrasound technique can be used to detect and accurately measure laser-induced microbubbles in tissue.

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

2007-03-01

402

Microsecond-long flash photography of laser-induced ablation of biliary and urinary calculi.  

PubMed

High-speed flash photographs of laser-induced fragmentation of biliary and renal calculi under water were obtained using one-microsecond-long dye-laser pulses for both illumination and ablation. The photographs show the presence of a bubble with irregularities on the surface that suggest the early presence of debris or microbubbles. Fragmentation occurs before the bubble collapses, suggesting that fragmentation is due to laser-induced acoustic transients rather than to collapse of a laser-induced cavitation bubble. PMID:3695781

Teng, P; Nishioka, N S; Farinelli, W A; Anderson, R R; Deutsch, T F

1987-01-01

403

Asymmetric acoustic gratings  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

404

Grating imaging scanning lithography for fabrication of large sized grating  

NASA Astrophysics Data System (ADS)

Diffraction grating is a high-resolution dispersion optical element. It has been widely used as the key component in optical spectroscopy, telecommunication multiplexing and laser systems, etc. Recently there is a growing demand for large-sized diffraction gratings in spectrometers industry, laser fusion facility, and its fabrication method is also a hot topic now. To fabricate large sized gratings, we have developed a grating imaging scanning lithography system. In this technology, the phase grating with jagged edge is used to generate diffractive beams and the spatial filter is used to select +/-1 order diffractive beams. Then two-beam interference on the substrate forms the grating fringes. At the same time, a 4f-system is used to form an identical image with clear boundary in the interference area. A high precision twodimensional mobile station, which enables the accurate positioning and move of the substrate, is utilized for complementary cyclical scanning, thus the image stitching errors are effectively eliminated. With this technology, we have fabricated a grating with period of 20?m and size of 100mm×100mm. In this paper the grating imaging scanning lithography procedure is described step by step. The principles and the experimental results are also explained in detail. With the characteristics of a simple structure, high energy utilization and stability, this new lithography technology should be an efficient way to fabricate large sized grating in the future.

Yu, Bin; Jia, Wei; Zhou, Changhe

2012-11-01

405

Lipid multilayer gratings.  

PubMed

The interaction of electromagnetic waves with matter can be controlled by structuring the matter on the scale of the wavelength of light, and various photonic components have been made by structuring materials using top-down or bottom-up approaches. Dip-pen nanolithography is a scanning-probe-based fabrication technique that can be used to deposit materials on surfaces with high resolution and, when carried out in parallel, with high throughput. Here, we show that lyotropic optical diffraction gratings--composed of biofunctional lipid multilayers with controllable heights between approximately 5 and 100 nm--can be fabricated by lipid dip-pen nanolithography. Multiple materials can be simultaneously written into arbitrary patterns on pre-structured surfaces to generate complex structures and devices, allowing nanostructures to be interfaced by combinations of top-down and bottom-up fabrication methods. We also show that fluid and biocompatible lipid multilayer gratings allow label-free and specific detection of lipid-protein interactions in solution. This biosensing capability takes advantage of the adhesion properties of the phospholipid superstructures and the changes in the size and shape of the grating elements that take place in response to analyte binding. PMID:20190751

Lenhert, Steven; Brinkmann, Falko; Laue, Thomas; Walheim, Stefan; Vannahme, Christoph; Klinkhammer, Soenke; Xu, Miao; Sekula, Sylwia; Mappes, Timo; Schimmel, Thomas; Fuchs, Harald

2010-02-28

406

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

407

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

408

Laser-induced microjet: wavelength and pulse duration effects on bubble and jet generation for drug injection  

NASA Astrophysics Data System (ADS)

The expansion of the laser-induced bubble is the main mechanism in the developed microjet injector. In this study, Nd:YAG and Er:YAG lasers are used as triggers of the bubble formation. The impact of the laser parameters on the bubble dynamics is studied and the performance of the injector is evaluated. We found that the main cause of the differences in the bubble behavior comes from the pulse duration and wavelength. For Nd:YAG laser, the pulse duration is very short relative to the bubble lifetime making the behavior of the bubble close to that of the cavitation bubble, while in Er:YAG case, the high absorption in the water and long pulse duration change the initial behavior of the bubble making it close to a vapor bubble. The contraction and subsequent rebound are typical for cavitation bubbles in both cases. The results show that the laser-induced microjet injector generates velocity which is sufficient for the drug delivery for both laser beams of different pulse duration. We estimate the typical velocity within 30-80 m/s range and the breakup length to be larger than 1 mm suitable for trans-dermal drug injection.

Jang, Hun-jae; Park, Mi-ae; Sirotkin, Fedir V.; Yoh, Jack J.

2013-05-01

409

Alignment of Liquid Crystals by Surface Gratings.  

National Technical Information Service (NTIS)

Square-wave grating structures with periodicities ranging from 3200 A to 12 micrometers were etched into fused quartz substrates, and the effect of such gratings on liquid crystal alignment was studied. Gratings with periodicities below 4 micrometers appe...

D. C. Shaver

1979-01-01

410

Raman and Laser-Induced Fluorescence Signatures of Isotopically Primitive and Normal IDPs  

NASA Astrophysics Data System (ADS)

Isotopically primitive IDPs have lower laser-induced fluorescence and wider Raman D bands than normal IDPs. Combined Raman/SIMS study suggests that there may be multiple carbonaceous carriers for the N-isotopic anomalies in primitive IDPs.

Wopenka, B.; Floss, C.

2012-03-01

411

Laser-Induced Fluorescence Measurements and Modeling of Nitric Oxide in Counterflow Diffusion Flames.  

National Technical Information Service (NTIS)

The feasibility of making quantitative nonintrusive NO concentration ((NO)) measurements in nonpremixed flames has been assessed by obtaining laser-induced fluorescence (LIF) measurements of (NO) in counterflow diffusion flames at atmospheric and higher p...

R. V. Ravikrishna

2000-01-01

412

Laser Induced Fluorescence Measurements and Modeling of Nitric Oxide in High-Pressure Premixed Flames.  

National Technical Information Service (NTIS)

Laser-induced fluorescence (LIF) has been applied to the quantitative measurement of nitric oxide (NO) in premixed, laminar, high-pressure flames. Their chemistry was also studied using three current kinetics schemes to determine the predictive capabiliti...

J. R. Reisel N. M. Laurendeau

1994-01-01

413

Stereoscopic Planar Laser-Induced Fluorescence Imaging at 500 kHz.  

National Technical Information Service (NTIS)

A new measurement technique for obtaining time- and spatially-resolved image sequences in hypersonic flows is developed. Nitric-oxide planar laser-induced fluorescence (NO PLIF) has previously been used to investigate transition from laminar to turbulent ...

J. Miller M. Webster N. Jiang P. M. Danehy S. B. Jones T. Meyer T. L. Medford W. Lempert

2011-01-01

414

Laser-induced damage thresholds at different temperature for optical devices  

NASA Astrophysics Data System (ADS)

Studies for temperature dependences of laser-induced damage thresholds for optical devise is introduced in this paper. Additionally, the temperature dependence of the laser-induced damage threshold of single-layer optical coatings as resent progress was clarified using Nd:YAG and Ti:sapphire lasers. The wavelengths of the lasers were 1064 nm and 800 nm and the pulse widths were 4 ns, 200 ps, 2 ps, and 100 fs. For pulses longer than a few picoseconds, the laser-induced damage threshold of coated substrates increased with decreasing temperature. This temperature dependence was reversed for pulses shorter than a few picoseconds. A flowchart was presented including the several mechanisms for laser damage mechanism. The differences in the temperature dependence are explained by the flowchart. As one of results in theoretical analysis, the electron resistivity i. e. electron mobility is key point to elucidate the temperature dependence of laser-induced damage threshold.

Mikami, Katsuhiro; Motokoshi, Shinji; Somekawa, Toshihiro; Jitsuno, Takahisa; Fujita, Masayuki; Tanaka, Kazuo A.

2013-07-01

415

Flow Property Measurement Using Laser-Induced Fluorescence in the NASA Ames Interaction Heating Facility.  

National Technical Information Service (NTIS)

The spectroscopic diagnostic technique of two photon absorption laser-induced fluorescence (TALIF) of atomic species has been applied to single-point measurements of velocity and static temperature in the NASA Ames Interaction Heating Facility (IHF) arc j...

B. J. Porter J. E. Carballo J. H. Grinstead

2011-01-01

416

CW-laser-induced thermal and mechanical damage in optical materials  

NASA Astrophysics Data System (ADS)

In this paper CW laser induced damage in optical materials were investigated using CW-CO2 laser. Inhomogeneous absorption will result in thermal stress in optical materials, which will induce crack, fusion of optical materials. These damages are related to microcracks and thermal properties of materials. It is shown that surface microcracks of optical materials is very important factor of CW laser induced damage, and the size of optical materials also has influence on damage thresholds. It is provided that CW laser induced damage mechanisms are thermal-stress accumulation damage and thermal-shock-stress damage. In addition, chemical etching was used to improve the damage resistance of optical materials, and CW laser induced damage thresholds of optical materials largely increased after 5 percent HCl solution etching.

Gong, Hui; Li, Cheng F.; Li, Zhong Y.

1999-04-01

417

Microwave interferometry of laser induced air plasmas formed by short laser pulses.  

National Technical Information Service (NTIS)

Applications for the interaction of laser induced plasmas with electromagnetic probes requires time varying complex conductivity data for specific laser/electromagnetic probe geometries. Applications for this data include plasma switching (Q switching) an...

P. W. Jungwirth

1993-01-01

418

Independent component analysis classification of laser induced breakdown spectroscopy spectra  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

419

Femtosecond laser-induced breakdown spectroscopy of surface nitrate chemicals.  

PubMed

Ultrashort laser-induced breakdown spectroscopy was used to detect the emission radiation from the breakdown of surface contaminants by a femtosecond laser pulse. This study focused on the detection of visible to near-infrared radiation signatures from molecular fragments of the nitro (NO(x)) group present in the breakdown plasma, where target chemicals of potassium nitrate (KNO(3)) and sodium nitrate (NaNO(3)) were used. Spectral signatures at a wavelength region around 410 nm were observed for both KNO(3) and NaNO(3), and were identified as the fluorescence transitions of the NO(x)-molecular structures. The signatures obtained were systematically analyzed and studied as functions of laser parameters. It is shown that for laser parameters used in this study, laser pulse durations ?1 ps were not as effective as shorter pulses in generating these signatures. A visible wavelength NO(x) signature and the extended high-intensity propagation of a femtosecond laser could be advantageous to detecting nitro-group energetic materials at standoff distances. PMID:23669773

Ahmido, Tariq; Ting, Antonio; Misra, Prabhakar

2013-05-01

420

Adhesion of polymer coatings studied by laser-induced delamination  

SciTech Connect

This paper concentrates on the laser-induced delamination technique, aimed at measuring the practical work of adhesion of thin polymer coatings on metal substrates. In this technique an infrared laser-pulsed beam is used to create an initial blister. Upon increasing the pulse intensity, the size of the blister grows, resulting in partial delamination of the film. In this work the blister profiles and the blister pressure were obtained from independent measurements. Alongside experiments, a simple model is developed to provide the equations necessary for calculating the blister strain energy, height, and the gas pressure inside the blister. The model is essentially based on an elastic behavior of the polymer film. The blister height and the blister pressure predicted by the model were confronted with the experimental observations and a fair agreement was found. The adhesion properties of the polyethylene terephthalate films on a steel substrate were characterized in terms of the maximum stress required for delamination and the practical work of adhesion. The relation between the two are discussed. Because the blister formation and subsequent delamination take place on a time scale of microseconds, it is argued that the viscous properties of the film do not manifest on this time scale and the contribution of plastic deformation of the film is rather small.

Fedorov, A.; Hosson, J.Th.M. de [Department of Applied Physics, Materials Science Centre, and the Netherlands Institute for Metals Research, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands)

2005-06-15

421

Ophthalmic manifestations of laser-induced eye injuries  

NASA Astrophysics Data System (ADS)

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

Belkin, Michael

1996-04-01

422

Experimental Studies of Laser-Induced Fluorescence of Kr^+  

NASA Astrophysics Data System (ADS)

We have succeeded in obtaining a laser-induced fluorescence (LIF) signal from Kr^+ in a low temperature Kr plasma discharge, using a diode laser, for a wavelength near 729nm. An atomic energy level scheme that is accessible to diode lasers is ^4D7/2-> ^4P5/2^0 -> ^4P5/2. The metastable state, ^4D7/2, one of several possible metastables states for excitation, proved to be sufficiently populated in the in a low temperature DC plasma discharge (Te˜1 eV, Ti˜1/40 eV, ni˜10^9 cm-3) to produced a high quality signal. The excitation wavelength is nominally 729 nm, and the detected photon is nominally 473 nm. We used an extended cavity diode laser in the Littrow configuration (Sacher-Lasertechnik TEC-100-0730-20). Successful completion of these experiments will provide a new ion velocity diagnostic for Kr ions which will aid in at least 3 basic plasma science experiments: 1) Hall Thruster ion plume measurements, 2) sheath formation in the case of multiple ion species plasmas (with 3 ion species), and 3) studies of the comparison between ion velocities of metastable state rare gas ions and known ground state ion mobilities.

Severn, Greg; Welsh, Tim; Hershkowitz, Noah

2012-10-01

423

Simultaneous elemental analysis system using laser induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

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

Body, Doug; Chadwick, Bruce L.

2001-03-01

424

Laser-induced breakdown spectroscopy in industrial and security applications  

SciTech Connect

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

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

2010-05-01

425

Multiphoton laser-induced-fluorescence studies of simple species  

SciTech Connect

Recent studies have demonstrated multiple-photon excitation of atomic species. Bischel and coworkers have provided a detailed description of two-photon excitation fluorescence in the detection of atoms generated in a low pressure discharge and its possible application as a diagnostic tool in flame and plasmas. It is also believed that such techniques can be useful in detecting molecular transients which are difficult to detect otherwise as demonstrated in two-photon laser-induced fluorescence (LIF) detection of NO. In this paper, we discuss our recent two-photon LIF studies on I and Br atoms, which are produced via laser photolysis of molecular precursors. The two-photon LIF study of HS and DS radicals is presented as a test case for the detection of other important radical species such as C/sub 2/H and CH/sub 3/, which are currently being investigated in our laboratory. In addition, excitation of three-photon resonances of I/sub 2/, N/sub 2/, and H/sub 2/ is discussed.

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

1983-01-01

426

Laser-induced ripple structures on Ni P substrates  

NASA Astrophysics Data System (ADS)

The ripple structures induced in Ni-P disks by 248 nm excimer laser pulses are experimentally investigated by varying laser fluence (175-270 mJ/cm 2 for 150 pulses) and pulse number (400-1000 pulses for 118 mJ/cm 2). A quantity [ Ra/( ?/2)] is proposed to characterize the real contact area at the head-disk interface. This quantity is defined as the ratio of roughness height Ra to half ripple period ( ?/2). The maximum shear stress and the plasticity index have been derived to analyze the ability for ripple structures to withstand stress and the head-ripple contact mode, respectively. Increasing fluence and pulse number may lead to an increase in ripple periodicity, and on the contrary, decreases in corresponding maximum shear stress, real contact area [ Ra/( ?/2)] and plasticity index. The laser parameters (fluence and pulse number) represent effective approaches to improve the tribology of the head-disk interface by controlling the laser-induced ripple pattern such as periodicity and roughness height. The laser irradiation with lower fluence and fewer pulses is helpful in producing the required ripple structure for laser texturing in magnetic media. This structure can meet the requirements of elastic contacts between head and disk, and less deformation under stress, although with a slight sacrifice in contact-area reduction.

Yu, J. J.; Lu, Y. F.

1999-07-01

427

Laser-induced electron diffraction for probing rare gas atoms.  

PubMed

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

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

2012-12-05

428

Laser induced crystallization of hydrogenated amorphous silicon-carbon alloys  

SciTech Connect

Laser induced crystallization of hydrogenated amorphous silicon carbon alloy (a-Si{sub 1-x}C{sub x}:H) films has been investigated by means of synchrotron x-ray diffraction. The a-Si{sub 1-x}C{sub x}:H films were deposited on (100) silicon wafers by very high frequency plasma enhanced chemical vapor deposition at 100 MHz in hydrogen diluted silane-methane gas mixtures. The substrate was kept at 250 deg. C or 350 deg. C and the stoichiometry was changed from x=0.20 to 0.63. The structural characterization of the as-grown films has been carried out by Rutherford backscattering (hydrogen concentration) and infrared spectroscopy (film ordering). The films were irradiated by a KrF excimer laser (248 nm) with varying energy density and number of pulses. After irradiation, the formation of SiC crystallites has been revealed by synchrotron x-ray diffraction. Besides SiC nanocrystals, the formation of crystalline Si and graphite is observed for under- (x<0.50) and over-stoichiometric (x>0.50) samples, respectively. The essential role played by hydrogen concentration and hydrogen bonding configuration in determining the melting threshold and the consequent SiC grain formation is highlighted.

Summonte, C.; Rizzoli, R.; Servidori, M.; Milita, S.; Nicoletti, S.; Bianconi, M.; Desalvo, A.; Iencinella, D. [CNR-IMM Section of Bologna, Via Gobetti 101, I-40129 Bologna (Italy); DICASM, University of Bologna, Viale Risorgimento 2, I-40136 Bologna (Italy)

2004-10-01

429

Multispectral-diode-laser-induced fluorescence biological particle sensor  

NASA Astrophysics Data System (ADS)

Laser-induced fluorescence (LIF) provides a real-time technique for detecting micron-size airborne pathogens. Early LIF biological particle sensors used harmonic generation of UV in solid-state lasers to excite fluorescence. UV diode lasers have several key advantages over traditional lasers: a greater selection of wavelengths for the efficient and selective excitation of specific fluorescent biological compounds; continuous output so that all sampled particles are interrogated; and the ability to combine several UV diode lasers emitting at different wavelengths into a compact multiple-wavelength source for simultaneously exciting several biofluorophores. The coincident detection of multiple biofluorophores is expected to markedly improve discrimination of airborne pathogens from non-biological background aerosols. In this paper, we describe BioLert 2x16C5+1 - a LIF bio-particle sensor with two diode lasers, detection of sixteen fluorescence emission bands bundled into five user-defined linear combinations, and an elastic scatter detector. BioLert 2x16C5+1 also features fluorescence photon counting for sensitivity sufficient to distinguish between single bacterial spores and similar size inert particles, improved signal processing for optimally distinguishing between airborne pathogens and harmless particles, and a highly integrated air sampling system.

Wilson, Geoffrey A.; DeFreez, Richard K.

2004-12-01

430

Laser induced damage and fracture in fused silica vacuum windows  

SciTech Connect

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

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

1996-11-01

431

Knudsen layer formation in laser induced thermal desorption  

NASA Astrophysics Data System (ADS)

Laser induced thermal desorption of Xe atoms into vacuum from a metal surface following the nano-second pulsed laser heating was investigated by the time-of-flight (TOF) measurement. The desorption flow was studied at a wide range of desorption flux by varying the initially prepared Xe coverage ? (1 ML = 4.5 × 1018 atoms/m2). At ? = 0.3 ML, the TOF of Xe was well represented by a Maxwell-Boltzmann velocity distribution, which is in good agreement with thermal desorption followed by collision-free flow. At ? > 0.3 ML, the peak positions of the TOF spectra were shifted towards the smaller values and became constant at large ?, which were well fitted with a shifted Maxwell-Boltzmann velocity distribution with a temperature TD and a stream velocity u. With TD fixed at 165 K, u was found to increase from 80 to 125 m/s with increasing ? from 1.2 to 4 ML. At ? > 4 ML, the value of u becomes constant at 125 m/s. The converging feature of u was found to be consistent with analytical predictions and simulated results based on the Knudsen layer formation theory. We found that the Knudsen layer formation in laser desorption is completed at Knudsen number Kn <0.39.

Ikeda, Akihiko; Matsumoto, Masuaki; Ogura, Shohei; Okano, Tatsuo; Fukutani, Katsuyuki

2013-03-01

432

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

2013-03-01

433

Analysis of liquid samples using laser-induced breakdown spectroscopy  

NASA Astrophysics Data System (ADS)

The application of Laser Induced Breakdown Spectroscopy (LIBS) to real-time, in-situ and remote analysis of trace amounts in liquid samples is described, to be used for example in harsh or difficult-to-reach environments within industry for the analysis of pollutants in water. Numerous elements, including a range of toxic heavy metals, have been measured over a wide range of concentrations. Detection limits usually are in the range of a few parts per million; for several elements even lower limits could be realized. The analysis system is based on a fiber delivery assembly which is capable to both deliver the laser light to, and to collect the micro-plasma light from the target area, up to 30 m. Alternatively, a telescopic arrangement for in a 'line-of-sight' arrangement was employed. In order to provide quantitative data in the evaluation of laser generated plasmas, parameters such as electron densities, plasma temperature, line shape functions, and others need to be known; their measurement and determination are outlined. For internal standardization and the generation of concentration calibration curves, reference lines of carefully chosen elements were used.

Samek, Ota; Liska, Miroslav; Kaiser, Josef; Krzyzanek, Vladislav; Telle, Helmut H.; Morris, Gavin W.; Beddows, David C.

1998-08-01

434

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

435

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

436

Visualization of plasma turbulence with laser-induced fluorescence (invited)  

SciTech Connect

Turbulence is a key factor limiting the performance of fusion devices. Plasma edge turbulence determines the boundary values of the plasma density and temperature, which in turn determine the internal gradients and controls global plasma transport. In recent years, significant progress has been made in modeling turbulence behavior in plasmas and its effect on transport. Progress has also been made in diagnostics for turbulence measurement; however, there is still a large gap in our understanding of it. An approach to improve this situation is to experimentally visualize the turbulence, that is, a high resolution 2-D image of the plasma density. Visualization of turbulence can improve the connection to theory and help validate theoretical models. One method that has been successfully developed to visualize turbulence in gases and fluids is planar laser-induced fluorescence. We have recently applied this technique to visualize turbulence and structures in a plasma. This was accomplished using an Alexandrite laser that is tunable between 700 and 800 nm, and from 350 to 400 nm with second harmonic generation. The fluorescence light from an argon ion transition has been imaged onto an intensified charged coupled device camera that is gated in synchronization with the laser. Images from the plasma show a rotating structure at 30 kHz in addition to small scale turbulence.

Levinton, Fred M.; Trintchouk, Fedor

2001-01-01

437

Resonance fluorescence spectroscopy in laser-induced cavitation bubbles.  

PubMed

Laser-induced breakdown spectroscopy (LIBS) in liquids using a double-pulse Q-switched Nd:YAG laser system has provided reliable results that give trace detection limits in water. Resonant laser excitation has been added to enhance detection sensitivity. A primary laser pulse (at 532 nm), transmitted via an optical fiber, induces a cavitation bubble and shockwave at a target immersed in a 10 mg l(-1)-100 mg l(-1) indium (In) water suspension. The low-pressure rear of the shockwave induces bubble expansion and a resulting reduction in cavity pressure as it extends away from the target. Shortly before the maximum diameter is expected, a secondary laser pulse (also at 532 nm) is fed into the bubble in order to reduce quenching processes. The plasma field generated is then resonantly excited by a fiber-guided dye laser beam to increase detection selectivity. The resulting resonance fluorescence emission is optically detected and processed by an intensified optical multichannel analyzer system. PMID:16520936

Koch, Sandra; Garen, Walter; Neu, Walter; Reuter, Rainer

2006-03-07

438

Behavior of laser-induced cavitation bubbles in liquid nitrogen  

NASA Astrophysics Data System (ADS)

Initial behavior and the subsequent motion of a bubble in liquid nitrogen are investigated experimentally using high-speed photography. A bubble is generated by focusing a pulsed ruby laser into liquid nitrogen at 78.0 K, changing the ambient pressures up to 253.2 kPa which corresponds to the applied pressure (or overpressure), ?p, being 147.1 kPa. When the energy level of the laser beam at the focus exceeds an irradiance threshold, for instance 5.4×1011 W/cm2 for ?p=4.9 kPa, the optical breakdown occurs in the liquid nitrogen, followed by a series of high-speed phenomena such as plasma formation, shock wave emission, and vapor bubble generation. It is found that during a very short period after the plasma formation a bubble grows nonspherically reflecting from the plasma shape, but the bubble volume itself varies with time in the same way for all cases performed in the present experiment. The liquid inertia is a dominant factor affecting the bubble growth, while the thermal effect becomes remarkable during the bubble collapse, resulting in the retardation of the bubble motion. The characteristic behavior of a laser-induced cavitation bubble in liquid nitrogen is significantly influenced by the phase change of vapor at the bubble surface as well as by the vapor pressure inside the bubble. Immediately after the bubble rebound, instabilities are amplified over the bubble surface similar to those caused in the water case.

Tomita, Y.; Tsubota, M.; Nagane, K.; An-Naka, N.

2000-11-01

439

Investigation of Ar+-laser-induced blood fluorescence spectra  

NASA Astrophysics Data System (ADS)

Laser-blood cells interaction was studied by Ar+ laser-induced animal (mouse) blood fluorescence spectra in vitro. The fluorescence spectra of the blood under various irradiated powers of Ar+ laser excitation are shown that there are very rich and sharp spectral peaks from 600 nm to 860 nm. These peaks are located at 616 nm, 666 nm, 708 nm, 739 nm, 752 nm, 766 nm, 800 nm, 812 nm and 844 nm. This may be due to the fact that there are various fluorophores in the blood and the ground electronic state of the fluorophores containing a large number of vibrational levels. In addition, 666 nm peak among them is the most prominent and is a larger change in the intensity under different power of Ar+ lasers excitation. It foretell that laser near a wavelength of 666 nm may be more effective to low lever laser therapy (LLLT). Furthermore, these experiments indicate that when the laser irradiated power density reaches to 30 mW/cm2 the blood cells are still not destroyed. The results may be significative for the choice of irrediation-wavelength in LLLT.

Gao, Shumei; Liu, Ying; Peng, Changde; Ni, Xiao-Wu; Lu, Jian

2003-12-01

440

Estimating intercellular surface tension by laser-induced cell fusion.  

PubMed

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. PMID:22146596

Fujita, Masashi; Onami, Shuichi

2011-12-06

441

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

442

Simulation of laser speckle reduction by using an array of diffraction gratings  

NASA Astrophysics Data System (ADS)

An array of diffraction gratings and a Random Phase Plate (RPP) are used to suppress laser speckle effect. Dynamic diffraction spots are generated on the surface of the RPP, after which the scattering lights are perceived by a detector. Speckle Contrast Ratio (CR) and Number of Independent Speckle Patterns (NISP) with different gratings rotation orientations (?), gratings frequencies (grooves per millimeter: f), diameters of laser beam (D), and distances between the array of diffraction gratings and the RPP (Z) are calculated based on ZEMAX simulations, and an optimized model is proposed.

Tong, Z. M.; Ouyang, G. M.; Gao, W. H.; Akram, M. N.; Kartashov, V.; Wang, K. Y.; Chen, X. Y.

2010-09-01

443

Bioanalytical and photophysical applications of sensitive nonlinear wave-mixing spectroscopy based on laser-induced gratings  

NASA Astrophysics Data System (ADS)

Nonlinear degenerate four-wave mixing is presented as a sensitive optical absorption-based detection and measurement technique for condensed-phase systems. By taking advantage of the inherent properties of this method, one can design a measurement system offering minimal optical path lengths (less than 100 mum) and miniscule probe volumes (often approaching just a few pico liters) using a single laser. This is possible because the laser output is split into two or more beams which are then redirected and focused to intersect at or near the focused waist of the beams. This ultra small probe volume makes this method inherently compatible with capillary flow systems and thin films. It also offers the additional benefit of minimizing the amount of sample required for study. This is particularly advantageous when the sample is difficult to obtain or may be dangerous to work with such as an enzyme, forensic sample or toxin. This method can also be used to study samples which themselves do not strongly absorb the light energy. Indirect detection is performed by measuring the effect the analyte of interest has on a co-solvated species which itself directly absorbs the laser light. By measuring the changes in the physical and chemical properties of this visualization agent, the presence of the analyte can be measured indirectly. The main effect giving rise to the degenerate four-wave mixing signal in liquid and other condensed-based systems is the conversion of light energy to heat by the absorbing medium. The subsequent temperature change induces an inhomogeneous change in the refractive index of the medium which diffracts the input beams to generate the signal beams. Because wave mixing is an optical absorption-based technique, it can be used simultaneously with other methods such as fluorescence to effectively measure the physical and chemical properties of an analyte.

Knittle, James Eugene

444

Photorefractive Moiré-like pattern generation and holographic grating spacing evaluation  

NASA Astrophysics Data System (ADS)

An experimental procedure for producing real-time Moiré-like patterns generation is demonstrated. The evaluation of the high frequency photorefractive sinusoidal grating spacing is shown to illustrate the technique capability. Moiré-like patterns are produced by the superposition of two rotated dynamic sinusoidal phase gratings by small angles in the photorefractive crystal Bi12TiO20.

dos Santos, P. A. M.; da Silva Nunes, L. C.

2001-07-01

445

Long-lived precession of spin gratings in n-doped GaAs  

Microsoft Academic Search

Transient grating experiments have been performed in lightly n-doped GaAs to measure population and spin dynamics. In the presence of a magnetic field perpendicular to the optical axis (Voigt geometry), the spin grating precesses, leading to a diffracted probe signal that oscillates at twice the precession frequency. In contrast to previous experiments in undoped [1] and heavily doped [2] samples,

Sam Carter; Zhigang Chen; Steven Cundiff

2006-01-01

446

Quantitative determination of element concentrations in industrial oxide materials by laser-induced breakdown spectroscopy  

Microsoft Academic Search

Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) method is employed for quantitative determination of oxide\\u000a concentrations in multi-component materials. Industrial oxide materials from steel industry are laser ablated in air, and\\u000a the optical plasma emission is collected by spectrometers and gated detectors. The temperature and electron number density\\u000a of laser-induced plasma are determined from measured LIBS spectra. Emission lines of aluminium (Al),

B. Praher; R. Rössler; E. Arenholz; J. Heitz; J. D. Pedarnig

447

Laser-induced discharges in vacuum and air: diagnostics of an extreme states of matter  

Microsoft Academic Search

Picosecond laser pulses at a wavelength of 1064 nm have been focused onto a copper cathode in coincidence with an electric field to produce a laser induced breakdown in vacuum and onto anode surface (Ag, Pd, W, AuNi electrodes) for laser-induced discharge in air. At a power density of about 3×10-13 W\\/cm2, the formation of local regions with high pressures

N. Vogel

1999-01-01

448

Stoichiometric changes in KH2PO4 crystals during laser-induced breakdown  

Microsoft Academic Search

The structure of KHPO single crystals (so-called KDP) irradiated with 3-ns, 355-nm laser pulses with fluences above the laser-induced breakdown threshold is studied by a combination of Raman scattering, photoluminescence, and soft x-ray absorption spectroscopies. We compare spectra from the as-grown material, surface and bulk laser-induced damage sites, as well as from KPO references. Results show that irradiation with fluences

R A Negres; S O Kucheyev; P DeMange; C Bostedt; T van Buuren; A J Nelson; S G Demos

2004-01-01

449

Decomposition of KH2PO4 crystals during laser-induced breakdown  

Microsoft Academic Search

The structure of KH2PO4 single crystals (so-called KDP) irradiated with ~3 ns, 355 nm laser pulses with fluences above the laser-induced breakdown threshold is studied by a combination of Raman scattering, photoluminescence, and soft x-ray absorption spectroscopies. We compare spectra from the as-grown material, surface and bulk laser-induced damage sites, as well as from KPO3 references. Results show that irradiation

R. A. Negres; S. O. Kucheyev; P. Demange; C. Bostedt; T. van Buuren; A. J. Nelson; S. G. Demos

2005-01-01

450

Hyperspectral laser-induced flourescence imaging for assessing internal quality of kiwi fruit  

Microsoft Academic Search

This paper describes an experimental study on non-destructive methods for predicting quality of kiwifruits using fluorescence imaging. The method is based on hyperspectral laser-induced fluorescence imaging in the region between 700 and 1110 nm, and estimates the kiwifruits quality in terms of internal sugar content and firmness. A station for acquiring hyperspectral laser-induced fluorescence imaging has been designed and carefully

Muhua Liu; Yifeng Liao; Xiaomei Zhou

2008-01-01

451

Computer-controlled measurements of laser-induced damage statistics on large optics  

Microsoft Academic Search

This paper presents data reduction on an experimental set-up that we have recently developed at CESTA, France. It has been implemented to analyze laser-induced damage on optics dedicated to the Megajoule laser project. Our goal is to measure the damage fluence on samples under tests, using a statistical approach on a very large number of sites. The laser-induced damage density