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Pulse Length (pulse + length)
Selected AbstractsSound production in two carapids (Carapus acus and C. mourlani) and through the sea cucumber tegumentACTA ZOOLOGICA, Issue 2 2006Eric Parmentier Abstract Parmentier, E., Fine, M., Vandewalle, P., Ducamp, J.-J. and Lagardčre, J.-P. 2006. Sound production in two carapids (Carapus acus and C. mourlani) and throught the sea cucumber teguments. ,Acta Zoologica (Stockholm) 87: 113,119 Carapus acus and Carapus mourlani are able to live inside sea cucumbers and sea stars respectively. Unlike other carapids whose sounds have been recorded (C. boraborensis, C. homei and Encheliophis gracilis), these two species have a central constriction in their swimbladder and are unlikely to encounter heterospecific carapids within their hosts. We evoked sound production in Carapus acus and Carapus mourlani by adding several individuals to a tank with a single host and found that their sounds differ substantially from the sounds emitted by other carapids in pulse length, peak frequency and sharpness of tuning (Q3 dB). Unlike the other carapids, C. mourlani and C. acus produce shorter and less repetitive sounds and do not produce sounds when they enter their host. Since sounds produced within a sea cucumber have the potential to be heard by distant carapids and are typically recorded outside the sea cucumber, we examined the effect of the sea cucumber tegument on acoustic transmission. Attenuation by the tegument was negligible at the frequencies within carapid sounds. Therefore, carapids have the potential to call from the relative safety of a sea cucumber without sacrificing the distance over which their transmissions are heard. [source] Extreme multielectron ionization of elemental clusters in ultraintense laser fieldsISRAEL JOURNAL OF CHEMISTRY, Issue 2 2007Andreas Heidenreich In this paper we present computational and theoretical studies of extreme multielectron ionization in Xen clusters (n = 55-2171, initial cluster radii R0 = 8.7-31.0 Å) driven by ultraintense Gaussian infrared laser fields (peak intensity IM = 1015 -1020 W cm,2, temporal pulse length , = 10-100 fs, and frequency v = 0.35fs,1). The microscopic approach, which rests on three sequential-parallel processes of inner ionization, nanoplasma formation, and outer ionization, properly describes the high ionization levels (with the formation of {Xeq+}n with q = 5-36), the inner/outer cluster ionization mechanisms, and the nanoplasma response. The cluster size and laser intensity dependence of the inner ionization levels are determined by a complex superposition of laser-induced barrier suppression ionization (BSI), with the contributions of the inner field BSI manifesting ignition enhancement and screening retardation effects, together with electron impact ionization. The positively charged nanoplasma produced by inner ionization reveals intensity-dependent spatial inhomogeneity and spatial anisotropy, and can be either persistent (at lower intensities) or transient (at higher intensities). The nanoplasma is depleted by outer ionization that was semiquantitatively described by the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity, and pulse length dependence of the outer ionization yield. [source] Formation and reactions of cluster ions from aromatic carboxylic acids together with amino acidsISRAEL JOURNAL OF CHEMISTRY, Issue 2 2001Anja Meffert The cluster formation of several aromatic carboxylic acids, ferulic acid, vanillic acid, sinapinic acid, and 3,4-dihydroxybenzoic acid was investigated by means of laser desorption into a supersonic beam followed by multiphoton ionization-time-of-flight mass spectrometry. The formation of not only homogeneous clusters, but also of heterogeneous clusters with some small amino acids was studied. The different neutral clusters formed in the supersonic expansion were ionized by a multiphoton process employing either nano- or femtosecond laser pulses. Strong differences in the detection of cluster ions due to the laser pulse length employed for multiphoton ionization were observed. Only femtosecond activation led to mass spectra with intense signals of the cluster ions. In addition, in the case of femtosecond ionization, protonated amino acids were detected in the mass spectra. As direct ionization of the free amino acids is not possible under the chosen ionization conditions because they lack an adequate chromophore, these protonated amino acids are assumed to be formed via an intracluster proton transfer in the heterogeneous dimer and subsequent decay of the ionized cluster (dissociative proton transfer). Such well-known processes for heterogeneous clusters consisting of a substituted aromatic molecule and small polar solvent molecules may be involved in the matrixassisted laser desorption ionization (MALDI) process. [source] Stimulated Raman scattering in Nd:SrWO4LASER PHYSICS LETTERS, Issue 1 2005H. Jelķnkovį Abstract Stimulated Raman scattering process in Nd:SrWO4 crystal was employed to frequency down-shift the fundamental frequency of a Nd:YAG mode-locked laser system. A single-pass configuration of Raman crystal was investigated for this purpose. After that Nd:SrWO4 laser was built and coherent pumping by alexandrite laser radiation was used. The simultaneous generation of stimulated Raman scattering was proofed for the case of Q-switching and mode-locking of Nd:SrWO4 Raman cavity. For Nd:YAG 50 ps long (1064 nm) pulsed pumping a single-pass first Stokes maximum energy and conversion efficiency were 1.6 mJ and 25% , respectively. With the free-running Nd:SrWO4 laser the maximum energy of 90 mJ at wavelength 1057 nm was obtained. Q-switching with the LiF:F,2 saturable absorber gave up to 1.3 mJ energy at the first Stokes frequency (1170 nm) in the pulse length of 3 ns. In mode-locking regime (with saturable absorber ML51 in dichlorethan or 3955 in ethanol), the total generated energy was 1.8 mJ and 2.4 mJ for ML51 and 3955 dyes, respectively. The SRS output at 1170 nm was approximately 20% of those values. (© 2005 by ASTRO, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Pilot clinical study of a novel minimally invasive bipolar microneedle radiofrequency device,LASERS IN SURGERY AND MEDICINE, Issue 2 2009Basil M. Hantash MD Abstract Background and Objectives Noninvasive bipolar and monopolar radiofrequency (RF) deep dermal heating devices have previously been described. A novel minimally invasive RF device employing a bipolar microneedle electrode system is introduced and its resultant thermal effects on human skin in vivo were characterized for the first time. Study Design/Materials and Methods An investigational 35 W RF device was configured to operate in bipolar mode delivering energy directly within the dermis using 5 microneedle electrode pairs with real-time feedback of tissue temperature for treatment control. Superficial cooling was achieved using a Peltier device. A range of pulse durations between 1 and 25 seconds, and lesion temperatures between 60 and 80°C were tested in vivo on 15 human subjects. Thermal effects were assessed histologically using either hematoxylin & eosin (H&E) or nitroblue-tetrazoliumchloride (NBTC) staining. Treatment effects and adverse events were also monitored clinically. Results The investigational bipolar RF device delivered controlled heating within dermal tissue. Histological staining with H&E revealed the presence of zones of denatured collagen within the reticular dermis. Lesions were generated at preselected temperatures between 60 and 80°C. Fractional lesions separated by zones of sparing as well as contiguous lesion patterns were demonstrated. Histological staining with H&E and NBTC revealed sparing of adnexal structures and adipose tissue. No major adverse events were observed. Conclusions A novel fractional RF device utilizing a minimally invasive bipolar microneedle delivery system for the treatment of human tissue was developed. Treatment of 15 human subjects illustrated the controlled creation of dermally located thermal coagulation zones, herein known as radiofrequency thermal zones. We discovered that varying the pulse length allowed for fractional sparing of dermal tissue. To our knowledge, this is the first report to describe use of a direct real-time temperature and impedance feedback system to control energy delivery during deep dermal heating. Lasers Surg. Med. 41:87,95, 2009. © 2009 Wiley-Liss, Inc. [source] Comparison of germanium oxide fibers with silica and sapphire fiber tips for transmission of erbium: YAG laser radiationLASERS IN SURGERY AND MEDICINE, Issue 8 2006Travis J. Polletto BS Abstract Background and Objectives Endoscopic applications of the Erbium:YAG laser have been limited due to the lack of a suitable optical fiber delivery system. The purpose of this study was to compare the transmission of Er:YAG laser radiation through germanium oxide trunk fibers with silica and sapphire fiber tips for potential use in contact tissue ablation during endoscopy. Study Design/Materials and Methods Er:YAG laser radiation with a wavelength of 2.94 µm, pulse length of 300 microseconds, pulse energies from 5 to 1,360 mJ, coupled into pulse repetition rates of 3,10 Hz, was through 1-m-long germanium oxide fibers with either 1-cm-long, 550-µm-diameter silica or sapphire tips. Results Transmission through the germanium oxide/sapphire fibers measured 65±5% compared with 55±4% for the germanium oxide/silica fibers (P<0.05). The damage threshold for the hybrid fibers averaged 309± 44 mJ and 126±43 mJ, respectively (n,=,7 fibers each) (P<0.05). The highest pulse energies transmitted through the fibers were 700 mJ and 220 mJ, respectively. Conclusions Improved index-matching of the trunk fiber and fiber tip at 2.94 µm resulted in higher transmission and damage thresholds for the germanium oxide/sapphire fibers. The germanium oxide/sapphire fiber may represent a promising mid-infrared optical fiber delivery system for use in endoscopic applications of the Er:YAG laser requiring a flexible, biocompatible, and robust fiber delivery system for contact tissue ablation. Lasers Surg. Med. 38:787,791, 2006. © 2006 Wiley-Liss, Inc. [source] Optically and electrically induced dissipation in quantum Hall systemsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2008G. Nachtwei Abstract We have studied the onset of dissipation in quantum Hall systems (QHSs), patterned in various geometries (Hall bars, meanders and Corbino rings) from wafers with heterojunctions (GaAs/GaAlAs) and HgTe quantum wells with adjacent HgCdTe barriers. The QH samples were excited by electrical pulses with pulse durations tP of 0.5 ns , tP , 180 ns or by illumination with electromagnetic waves of 1.7 THz , f , 2.5 THz. These waves were either emitted coherently by a pulsed p-Ge laser system or by a thermal source. In the case of excitation by electric pulses, it is necessary to exceed a certain critical pulse length which is a function of various extrinsic parameters and sample properties. For no dissipation occurs inside the QHSs. Also, using THz illumination, the QHSs can be driven to dissipation. We found different mechanisms to be responsible for the photoresponse (PR) of the QHSs: non-resonant (bolometric) and resonant (cyclotron resonance) contributions to the PR of the QHSs. First attempts to develop a quantitative model for the observed data are made. We are able to describe a part of the observations by either a drift model or a two-level model. The quantitative agreement of these calculations with the measured data is, however, limited. This is due to the simplicity of the models applied so far and to the complex behaviour of QHSs when nonlinearly excited. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Plasma-Assisted Atomic Layer Deposition of Al2O3 at Room TemperaturePLASMA PROCESSES AND POLYMERS, Issue S1 2009Tommi O. Kääriäinen Abstract A new design of plasma source has been used for the plasma-assisted atomic layer deposition (PA-ALD) of Al2O3 films at room temperature. In this PA-ALD reactor the plasma is generated by capacitive coupling directly in the deposition chamber adjacent to the substrate but can be separated from it by a grid to reduce the ion bombardment while maintaining the flow of radicals directly to the substrate surface. During the ALD cycle a mixture of nitrogen and argon was introduced into the reactor to act as a purge gas between precursor pulses and to facilitate the generation of a plasma during the plasma cycle. Sequential exposures of TMA and excited O2 precursors were used to deposit Al2O3 films on Si(100) substrates. A plasma discharge was activated during the oxygen gas pulse to form radicals in the reactor space. The experiments showed that the growth rate of the film increased with increasing plasma power and with increasing O2 pulse length before saturating at higher power and longer O2 pulse length. The growth rate saturated at the level of 1.78 Å·cycle,1. EDS analysis showed that the films were oxygen rich and had carbon as an impurity. This can be explained by the presence of bonds between hydrocarbons from the unreacted TMA precursor and excess oxygen in the film. ATR-FTIR spectroscopy measurements indicated a change in growth mechanism when the distance between the location of the radical generation and the substrate was varied. A similar effect was observed with the use of different plasma power levels. [source] The effect of material, thermal and laser conditioning on the damage threshold of type II tripler-cut DKDP crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2008Shao-Tao Sun Abstract By using the traditional temperature-reduction method, KD2PO4 (DKDP) crystals were grown from 85%-deuterated aqueous solution synthesized by different kind of KH2PO4 (KDP) raw materials. An experimental technique was employed to measure the variation of bulk damage threshold in plates of DKDP crystals. Bulk laser damage in unconditioned, thermal-conditioned and laser-conditioned type II tripler-cut DKDP crystals has been studied using 1064 nm (,) and 355 nm (3,) laser at pulse lengths of 5ns, 5ns respectively. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Hybrid germanium/silica optical fibers for endoscopic delivery of erbium:YAG laser radiationLASERS IN SURGERY AND MEDICINE, Issue 1 2004Charles A. Chaney MS Abstract Background and Objectives Endoscopic applications of the erbium (Er):YAG laser have been limited due to the lack of an optical fiber delivery system that is robust, flexible, and biocompatible. This study reports the testing of a hybrid germanium/silica fiber capable of delivering Er:YAG laser radiation through a flexible endoscope. Study Design/Materials and Methods Hybrid optical fibers were assembled from 1-cm length, 550-,m core, silica fiber tips attached to either 350- or 425-,m germanium oxide "trunk" fibers. Er:YAG laser radiation (,,=,2.94 ,m) with laser pulse lengths of 70 and 220 microseconds, pulse repetition rates of 3,10 Hz, and laser output energies of up to 300 mJ was delivered through the fibers for testing. Results Maximum fiber output energies measured 180±30 and 82±20 mJ (n,=,10) under straight and tight bending configurations, respectively, before fiber interface damage occurred. By comparison, the damage threshold for the germanium fibers without silica tips during contact soft tissue ablation was only 9 mJ (n,=,3). Studies using the hybrid fibers for lithotripsy also resulted in fiber damage thresholds (55,114 mJ) above the stone ablation threshold (15,23 mJ). Conclusions Hybrid germanium/silica fibers represent a robust, flexible, and biocompatible method of delivering Er:YAG laser radiation during contact soft tissue ablation. However, significant improvement in the hybrid fibers will be necessary before they can be used for efficient Er:YAG laser lithotripsy. Lasers Surg. Med. 34:5,11, 2004. © 2004 Wiley-Liss, Inc. [source] | ||||||||||