Dual Pulses Research Articles

Combination of Er:YAG laser and CO2 laser treatment on skin tissue.

Skin is the most important organ in our body, as it protects us from external environmental effects. Study the ability of the skin to stretch and the histological examinations of irradiated tissues have significant values in scientific and medical applications. Only a few studies have been done to study the correlation between epidermis ablation and the changes that occur at dermal levels when using dual lasers in ablative resurfacing mode. The aim of this work is to determine this correlation and to estimate the effects of multiple pulses on induced collagen remodeling and the strength of skin exposed with dual lasers in an in vivo rat model. All laser exposures led to mark improvement in the skin's strength compared to their own controls. The histological investigation indicated that there was a thickness loss in the epidermis layer with the induction of deep collagen coagulation in the dermis layer as the dual laser pulses increased. Additionally, more collagen fibers were remolded in the treated samples by dual wavelengths. We conclude that by combining dual lasers with multiple pulses targeted at not only the epidermis layer of the skin, it could also induce some heat diffusion in the dermis layer which causes more coagulation of collagen fibers. The tensile results confirmed by our histological data demonstrate that the strength of irradiated skin with dual wavelengths increased more than using both lasers separately on the skin tissue since more collagen is induced.

Dissociative ionization of methane in an elliptical pulse shaped laser field

The effect of strong femto-second laser pulses on the dissociation probability of methane has been investigated analytically in various arrangements. The ellipticity dependence of the dissociation probability at intensities from 1014Wcm−2 to 1016Wcm−2 for Ti:Sapphire laser is presented. A reliable calculation of the dissociation probability based on 3D time-dependent Schrodinger equation with an improved model of time-dependent density-functional theory is presented. These calculations are carried out for three different cases of elliptically polarized laser pulse, optimum convolution of dual short pulses, and two-color mixed nonresonant laser pulses. It is found that the rescattering contribution of the laser pulses to the fragmental yields is more remarkable for ε=0.2, at 1015Wcm−2 laser intensity. Furthermore, by using the dual pulses combination for three proposed conditions, extracted by semi-classical approach, the dissociation rates up to 78% is achieved. In addition, by using a two-color mixed laser pulse, the total dissociation probability is improved up to 50% in comparison to a single pulse.

Periodical energy oscillation and pulse splitting in sinusoidal volume holographic grating.

This paper presents dynamical diffraction properties of a femtosecond pulse in a sinusoidal volume holographic grating (VHG). By the modified coupled-wave equations of Kogelnik, we show that the diffraction of a femtosecond pulse on the VHG gives rise to periodical energy oscillation and pulse splitting. In the initial stage of diffraction, one diffracted pulse and one transmitted pulse emerge, and energy of the transmitted pulse periodically transfers to the diffracted pulse and vice versa. In the latter stage, both the diffracted and transmitted pulses split into two spatially separated pulses. One pair of transmitted and diffracted pulses propagates in the same direction and forms the output diffracted dual pulses of the VHG, and the other pair of pulses forms the output transmitted dual pulses. The pulse interval between each pair of dual pulses is in linearly proportional to the refractive index modulation and grating thickness. By the interference effect and group velocity difference we give explanations on the periodical energy oscillation and pulse splitting respectively.

The influence of wavelength, temporal sequencing, and pulse duration on resonant infrared matrix-assisted laser processing of polymer films

We have carried out a systematic investigation of laser ablation plume interactions in resonant infrared matrix-assisted pulsed laser evaporation. The laser source utilized in this study was a mid-infrared OPO capable of dual sequential ns pulses with adjustable delay ranging from 1 to 100 μs. This unique capability enabled us both to probe the ablation plume with a second laser pulse, and to effectively double the laser fluence. The primary ablation target used for this study consisted of poly(methyl methacrylate) dissolved in a binary mixture of methanol and toluene. Both the critical thermodynamic and optical properties of the binary mixture were determined and used to interpret our results. We found that deposition rates associated with single pulse irradiation tracks with the optical absorption coefficient in the spectral range from 2,700 to 3,800 nm. In the case of dual sequential pulses, discrepancies in this trend have been linked to the rate of change in the optical absorption coefficient with temperature. The influence of fluence on deposition rate was found to follow a sigmoidal dependence. Surface roughness was observed to have a diametrically opposed trend with pulse delay depending on whether the OH or CH vibrational mode was excited. In the case of CH excitation, we suggest that the rougher films are due to the absorbance of the second pulse by droplets within the plume containing residual solvent which leads to the formation of molecular balloons and hence irregularly shaped features on the substrate.

Mitigation of energetic ion debris from Gd plasma using dual laser pulses and the combined effect with ambient gas

For the next-generation beyond extreme ultraviolet lithography (EUVL) sources, gadolinium (Gd) plasma with emission wavelength at 6.7 nm seems to be the leading candidate. Similar to the Sn target 13.5 nm light source, ion debris mitigation is one of the most important tasks in the laser-produced Gd plasma EUV source development. In this paper, a dual-laser-pulse scheme, which uses a low energy pulse to produce a pre-plasma and a main pulse after a time delay to shoot the pre-plasma, is employed to mitigate the energetic ion generation from the source. Optimal conditions (such as pre-pulse energy and wavelength, and the time delay between the pre-pulse and the main pulse for mitigating the ion energy) are experimentally obtained, and with the optimal conditions, the peak of the ion energy is found to be reduced to 1/18 of that of a single laser pulse case. Moreover, the combined effect by applying ambient gas to the dual-pulse scheme for ion debris mitigation is demonstrated, and the result shows that the yield of Gd ions is further reduced to around 1/9 of the value for the case with dual laser pulses.

Investigation of intense femto-second laser ionization and dissociation of methane with time-dependent density-functional approach

Three dimensional calculations of electronic dynamics of CH4 in a strong laser field are presented with time-dependent density-functional theory. Time evolution of dipole moment and electron localization function is presented. The dependence of dissociation rate on the laser characters is shown and optimal effective parameters are evaluated. The optimum field leads to 76% dissociation probability for Gaussian envelope and 40fs (FWHM) at 1016Wcm−2. The dissociation probability is calculated by optimum convolution of dual short pulses. By combining of field assisted dissociation process and Ehrenfest molecular dynamics, time variation of bond length, velocity and orientation effect are investigated.

Measuring quantum coherence in bulk solids using dual phase-locked optical pulses

Electronic and phonon coherence are usually measured in different ways because their time-scales are very different. In this paper we simultaneously measure the electronic and phonon coherence using the interference of the electron-phonon correlated states induced by two phase-locked optical pulses. Interferometric visibility showed that electronic coherence remained in a semiconducting GaAs crystal until ~40 fs; in contrast, electronic coherence disappeared within 10 fs in a semimetallic Bi crystal at room temperature, differing substantially from the long damping time of its phonon coherence, in the picosecond range.

Spectroscopic Diagnostics for Plasma Produced by Exposure of a Target in Liquid to Dual Laser Pulses

We have studied the optical emission spectra of a laser plasma formed when targets made from zinc alloys and positioned in a liquid are exposed to dual laser pulses, for different delays between pulses. We give estimates of the electron temperature and electron concentration for the plasma in the liquid from the Boltzmann and Saha–Boltzmann equations and the Stark line broadening. We have established that as the interpulse interval increases, fractionation of the alloying elements entering the plasma is enhanced.

Slower Piezo1 Inactivation in Dehydrated Hereditary Stomatocytosis (Xerocytosis)

Slower Piezo1 Inactivation in Dehydrated Hereditary Stomatocytosis (Xerocytosis)

Production of layered coatings of Fe-Ni alloy for enhanced corrosion protection

Layered Fe-Ni alloy coatings have been galvanostatically developed on copper using dual and triple square current pulse from acid sulfate bath. The cyclic cathode current density (CCCD) and number of layers have been optimized for enhanced performance of the coatings against corrosion. Corrosion behavior of the coatings is evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy methods in 1 M HCl solution. The polarization study confirms that coatings developed using triple square pulses are more corrosion resistant than those deposited by dual square pulses. The improved corrosion behavior of layered coatings is due to the changed intrinsic electric properties evidenced by the electrochemical impedance spectroscopy. Under optimal conditions, the coatings developed using dual and triple square current pulse have been found to be by about 23 and 57 times, respectively, more corrosion resistant than the monolithic alloys. Surface morphology and layered coatings have been examined by scanning electron microscopy. Saturation of corrosion resistance at a high degree of layering was found, which is attributed to a shorter relaxation time for redistribution of metal ions during plating.

Analyses of heavy metals by soil using dual-pulsed laser induced breakdown spectroscopy

The heavy metal elements contained in soil samples which are collected from Changchun train station, CUST campus, South Lake and Jingyue Lake park are separately analyzed by using the orthogonal dual laser pulses induced breakdown spectroscopy (DP-LIBS). The elements Mn, Cr, Cu and Pb are qualitatively analyzed according to the LIBS spectral intensity. It is shown that the intensity of the spectrum is greatly enhanced by using the DP-LIBS and the enhancement is closely related to the delay time between the double pulses. Enhancement variation with delay time presents double-peak changing when 532 nm and 1064 nm laser pulse energies are 70 mJ and 100 mJ respectively. The enhancement of Mn I 406.4 nm is 2.75 at a delay time of 20 s and it is 2.4 at a delay time of 30 s when the second peak appears. The enhancement mechanism of orthogonal pre-ablation DP-LIBS is further discussed.

Nanoplasmonic electron acceleration in silver clusters studied by angular-resolved electron spectroscopy

The nanoplasmonic field enhancement effects in the energetic electron emission from few-nm-sized silver clusters exposed to intense femtosecond dual pulses are investigated by high-resolution double differential electron spectroscopy. For moderate laser intensities of 1014 W cm−2, the delay-dependent and angular-resolved electron spectra show laser-aligned emission of electrons up to keV kinetic energies, exceeding the ponderomotive potential by two orders of magnitude. The importance of the nanoplasmonic field enhancement due to resonant Mie-plasmon excitation observed for optimal pulse delays is investigated by a direct comparison with molecular dynamics results. The excellent agreement of the key signatures in the delay-dependent and angular-resolved spectra with simulation results allows for a quantitative analysis of the laser and plasmonic contributions to the acceleration process. The extracted field enhancement at resonance verifies the dominance of surface-plasmon-assisted re-scattering.

Modeling of dual fluorescence kinetics for 9-anthryl-substituted oligothiophenes

Expressions for time-dependent level populations in four- and five-level molecular models are obtained for the case of radiative and nonradiative decay from an initially populated state corresponding to the highest energy of the molecule. The two lowest energy levels in the models are assigned to vibrational levels of a molecular subsystem in the ground state; the others, to levels of the molecule in the excited electronic state. Examples of applying the obtained expressions to establish the formation mechanism for dual fluorescence pulses that accompany the phototransfer of a H-bond proton and other conformational transformations of molecules are presented.

Gastric Neuromodulation With Enterra System for Nausea and Vomiting in Patients With Gastroparesis

Gastric electrical stimulation (GES) has been introduced for treating gastric motility disorders, such as gastroparesis, and obesity. A special method of GES using high frequency-short pulses, called Enterra® Therapy, has been clinically applied to treat nausea and vomiting in patients with gastroparesis. However, its mechanisms are not well understood. General methodologies of GES published in the literature are systematically reviewed and their main effects and application are presented. The major part of this review is focused on Enterra Therapy since this is the only method that has been used clinically. A number of different GES methods have been proposed. GES with long pulses or dual pulses, but not short pulses, are able to alter (enhance or inhibit) such parameters of gastric motility as gastric slow waves and gastric emptying. Synchronized GES has been reported to improve antral contractions. GES with high frequency-short pulses, or Enterra Therapy, is known to improve nausea and vomiting in patients with gastroparesis and has a response rate of 50-70%. Improved gastric accommodation, direct enteric nervous system effects, enhanced vagal activity, and activation of central neurons are believed to be the underlying mechanisms involved in the antiemetic effect of this therapy. GES with high frequency-short pulses effectively reduces nausea and vomiting in patients with gastroparesis. This antiemetic effect could be mediated via enteric, autonomic, and/or central neural mechanisms. Further systematic and controlled studies are needed to improve the efficacy of Enterra Therapy and to understand its mechanisms of action.

Single- and dual-pulse oscillation in a passively Q-switched Nd:YAG microchip laser

Experimental investigation of single and dual pulses in a passively Q-switched Nd:YAG microchip laser with a Cr4+:YAG saturable absorber has been reported. The dual pulses consist of a main and a satellite pulse with respective spectra, intensities, and durations. It is found that the preponderant oscillating mode gives birth to the main pulse, and the other oscillating mode corresponds to the satellite pulse. Our results demonstrate that the dual-pulse emission results from double-longitudinal-mode oscillation in high pump regime.

Influence of Molecular Gases on the Lasing on the Self-Terminating $He~\left(2^{1}P_{1}^{0}-2^{1}S_{0}\right)$ Transition

Excitation with single and dual electron-beam pulses was used to investigate into the lasing on the self-terminating <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">He</i> (2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sup> -2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) transition in mixtures of helium with various molecules. In pure helium the maximum lasing duration was found to be equal to 50 ns, this time being fairly well coincident with the calculated lasing duration. Restoration of lasing in the second pulse was observed following a time Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> >; 1.25 μs. Foreign molecular species admixed to helium enhance the relaxation rate of the metastable He(2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) state, thus making the time Δ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">tmin</i> shorter until the pulses finally merge together. In the mixtures of helium with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">NH</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> excited with 650-ns electron-beam pulses, the lasing duration of 600 ns was observed. Such duration indicates realization of a collisional quasi-continuous lasing mode.

Gastric electrical stimulation reduces visceral sensitivity to gastric distention in healthy canines

The aim of this study was to investigate the effects and mechanisms of gastric electrical stimulation (GES) on proximal stomach distention-induced visceral sensitivity. Isobaric gastric distention was performed using a barostat system in 8 normal and 6 vagotomized dogs and animal behaviors were noted and graded. The normal dogs were studied in 4 sessions: control (no GES), short pulse GES, long pulse GES, and dual-pulse GES, and the vagotomized dogs were studied in three sessions: control (no GES), long pulse GES and guanethidine. It was found that: 1) proximal stomach distention-induced behavioral changes were mediated by vagal and sympathetic pathways. The total behavior score (TBS) was 40.6±7.4 in the controls, 15.3 ±8.9 in vagotomized dogs (P=0.006 vs. control) and 8.8±0.9 in the vagotomized dogs with guanethidine (P=0.04 vs. vagotomy). The behavioral changes were mediated via the vagal pathway at distention pressures below 20mmHg, but mediated via both the vagal and sympathetic pathways at distention pressures equal to and above 20mmHg. 2) GES with long pulses or dual pulses but not short pulses reduced the distention-induced behavioral score (P=0.003, P=0.006 and P=0.7, respectively) and the effects of GES of long pulses might be mediated via the vagal and sympathetic pathways. In conclusion, gastric distention-induced visceral sensitivity is mediated via the vagal pathway at low distention pressures but via both vagal and sympathetic pathways at high distention pressures. GES with long but not short pulses reduces distention-induced visceral sensitivity.

Implementation of 3 T Lactate-Edited 3D 1H MR Spectroscopic Imaging with Flyback Echo-Planar Readout for Gliomas Patients

The purpose of this study was to implement a new lactate-edited 3D 1H magnetic resonance spectroscopic imaging (MRSI) sequence at 3 T and demonstrate the feasibility of using this sequence for measuring lactate in patients with gliomas. A 3D PRESS MRSI sequence incorporating shortened, high bandwidth 180° pulses, new dual BASING lactate-editing pulses, high bandwidth very selective suppression (VSS) pulses and a flyback echo-planar readout was implemented at 3 T. Over-prescription factor of PRESS voxels was optimized using phantom to minimize chemical shift artifacts. The lactate-edited flyback sequence was compared with lactate-edited MRSI using conventional elliptical k-space sampling in a phantom and volunteers, and then applied to patients with gliomas. The results demonstrated the feasibility of detecting lactate within a short scan time of 9.5 min in both phantoms and patients. Over-prescription of voxels gave less chemical shift artifacts allowing detection of lactate on the majority of the selected volume. The normalized SNR of brain metabolites using the flyback encoding were comparable to the SNR of brain metabolites using conventional phase encoding MRSI. The specialized lactate-edited 3D MRSI sequence was able to detect lactate in brain tumor patients at 3 T. The implementation of this technique means that brain lactate can be evaluated in a routine clinical setting to study its potential as a marker for prognosis and response to therapy.

SKS and SPdKS sensitivity to two‐dimensional ultralow‐velocity zones

Seismic wave propagation through two‐dimensional core‐mantle boundary (CMB) ultralow‐velocity zones (ULVZs) is modeled using a global pseudospectral algorithm. Seismograms are synthesized for several types of ULVZ models to investigate the effect of these structures on SKS and SPdKS phases. One‐dimensional models and two‐dimensional models with different, quasi‐1‐D velocity structures on the source and receiver sides of the CMB provide a baseline for comparison with other 2‐D models. Models with finite length ULVZs are used to test the sensitivity of the SPdKS travel time and waveform to different portions of the P diffracted wave path. This test shows that SPdKS waves are only sensitive to ULVZs with lengths &gt;100 km. Our results give three tools for identifying and characterizing 2‐D ULVZ structures. First, dual SPdKS pulses indicate exposure to at least two separate CMB velocity structures, either different source and receiver‐side CMB velocities or different adjacent velocity regions for which Pdiff inception occurs outside of and propagates into a ULVZ. Second, high‐amplitude SKS precursors indicate a very “strong” (i.e., thick and/or large velocity perturbations) ULVZ. Hence, the absence of SKS precursors in most previous ULVZ studies indicates that very strong, sharp ULVZs are not common. Third, mean SPdKS delays relative to PREM constrain the minimum ULVZ strength and length combinations required to produce a given travel time delay.

The perils of plasticity: dual resource pulses increase facilitation but destabilize populations of small-bodied cavity-nesters

Resource pulses within structured communities can lead to changes in the ecological roles of community members, particularly for species that exhibit plasticity in resource use. The red-breasted nuthatch Sitta canadensis is a facultative excavating cavity-nester that forages on seeds and insects, thus exhibits plasticity in both nesting habits and diet. In a long-term study of cavity-nesting vertebrates, we used point counts, and nest and vegetation surveys to examine the effects of two resource pulses of mountain pine bark beetle prey Dendroctonus ponderosae and tree cavities via excavator populations, on population densities and cavity reuse of red-breasted nuthatches, from 1997–2006. We observed a doubling in mean nut-hatch densities from 0.12 to 0.24 individuals ha−1 then a collapse later in the decade to 50% below endemic levels (0.06 individuals ha−1). These regional fluctuations were positively correlated with densities of trees recently infected by bark beetles. Because nuthatches range over large areas in winter, this regional correlation suggests that populations responded to the increase in winter food supply. At the site scale, general linear mixed effects models showed that nuthatch populations increased following years of high densities of downy woodpeckers Picoides pubescens, suggesting that downy woodpeckers were important facilitators, via cavity excavation. Type of nesting cavity used by nuthatches varied during the pulse, such that the use of existing cavities (in lieu of excavation) increased on sites that had harboured downy woodpecker nests in the previous year. We conclude that increased densities of cavity excavators allowed facultative excavators to increase their reuse of cavities, which may have contributed to the dramatic increases in nuthatch populations. However, nuthatch populations collapsed after the boom suggesting that this dual resource pulse may have destabilized populations by enabling densities to reach unsustainable levels. Thus, plasticity in resource use can have serious costs as well as benefits.