Suchergebnisse

It is widely accepted that the lower mantle consists of mainly three major minerals-ferropericlase, bridgmanite and calcium silicate perovskite. Ferropericlase ((Mg,Fe)O) is the second most abundant of the three, comprising approximately 16-20 wt% of the lower mantle. The stability of ferropericlase at conditions of the lowermost mantle has been highly investigated, with controversial results. Amongst other reasons, the experimental conditions during laser heating (such as duration and achieved temperature) have been suggested as a possible explanation for the discrepancy. In this study, we investigate the effect of pulsed laser heating on the stability of ferropericlase, with a geochemically relevant composition of Mg0.76Fe0.24O (Fp24) at pressure conditions corresponding to the upper part of the lower mantle and at a wide temperature range. We report on the decomposition of Fp24 with the formation of a high-pressure (Mg,Fe)(3)O(4)phase with CaTi2O4-type structure, as well as the dissociation of Fp24 into Fe-rich and Mg-rich phases induced by pulsed laser heating. Our results provide further arguments that the chemical composition of the lower mantle is more complex than initially thought, and that the compositional inhomogeneity is not only a characteristic of the lowermost part, but includes depths as shallow as below the transition zone. ; Funding Agencies|Federal Ministry of Education and Research, Germany (BMBF)Federal Ministry of Education & Research (BMBF) [5K16WC1, 05K19WC1]; Deutsche Forschungsgemeinschaft (DFG)German Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University faculty grant SFO-Mat-LiU [2009 00971]

Exact and approximate solutions to the non-stationary problem on the heat conduction in a semi-bounded body exposed to a pulsed laser radiation flow have been obtained. The action of rectangular, triangular and parabolic laser radiation pulses on this body was investigated. Polynomial relations have been constructed on the basis of the boundary-characteristic method with introduction into consideration of the temperature-disturbance front, and they made it possible to obtain practically exact solutions for the temperature function and its time derivative at both the stages of heating and cooling of the body. It is shown by some examples that the success in solving problems on the pulsed plasma heating of bodies is associated in many respects with the necessity of definition of the time law of movement of the temperature-disturbance front with the use of the Pade diagonal approximation, which excludes, practically completely, the divergence of the power series defining the law of movement of this front, in particular, in small time intervals. The approach proposed for solving heat-conduction problems with the second-kind boundary condition allows one to simply and effectively find solutions for isotherms and lines of equal heating and cooling. Analysis of the results obtained allows the conclusion that the effectiveness of solving various technological problems, based on the use of pulsed laser radiation, is determined by the success in solving the problems on control of the time shape of a laser pulse and determination of the temperature fields in the body on the basis of polynomial representations.

This paper deals with pulsed laser welding of aluminum using an Nd:YAG laser with wavelength 1.06 μm. Technically pure aluminum (95.50 wt. %) was used as the welded material. Eighteen welds (penetration passes) were fabricated in the experiment. Optical microscopy was used to assess the influence of changes in the parameters of the pulsed laser on the quality and geometry of the penetration passes of aluminum and on the hardness measurement through the interface of the welds. The results show that the geometry of the penetration passes was influenced above all by the position of the beam focus.

The modern military industry demands the most innovative and high-quality metals and alloys, as well as processing technologies. Iron and its alloys are a common material used for different types of weapons and military equipment. Lasers have been widely used in the metal surface processing, but the changes that occur on laser treated metal surfaces have not yet been sufficiently investigated. A study of morphological and chemical changes on the metal surface induced by Nd:YAG laser treatment in ambient air is presented. A pulsed Nd:YAG laser (1064 nm, Gaussian spatial profile, FWHM 8 ns, energy up to 525 mJ, beam diameter of 1-10 mm and fluence up to 3.5 J/cm 2 ) was used. Micro-morphological analyses of sample surfaces before and after laser treatment process were performed by optical and SEM microscopies. EDX method was used for chemical analyses and Spectra colorimeter for investigation of induced color changes. The laser irradiation effects were studied as a function of two laser parameters, number of laser pulses and laser fluencies, around and over the damage threshold. The results show that there are significant differences depending on these laser parameters.

The US Air Force has need of parabolic-shaped membrane mirrors for surveillance satellites. The current polymer membrane technology has been unable to overcome shape deformation problems caused by intrinsic stresses from the membrane casting and mounting processes. One proposed solution was to coat the membrane mirrors with a stressed coating to compensate for shape deformations. Thus, the research presented in this dissertation produced controlled-stress large-area pulsed laser deposition (PLD) grown thin films on polymer substrates and investigated optical time-of-flight (TOF) sensor systems and Raman spectroscopy for control for the PLD process with respect to thin film stress. Initially, the PLD-grown film stress was controlled using a constant combination of deposition parameters. Also, the velocity was extracted from the optical TOF data and indicated film stress. As such, the velocity was used to control the laser fluence in order to compensate for slight variations in deposition conditions, which improved the film stress run-to-run stability. Additionally, iterative and theoretical experiments produced large-area YSZ films with less than ten percent total thickness variations. Combining the controlled-stress and large-area aspects produced desirable compensations in shape to the polymer substrates. Finally, Raman spectroscopy was shown to be compatible with the PLD.

In this study, mixing of zinc oxide (ZnO) nanoparticles with iron oxide(Fe2O3) at (0, 0.1, 0.3, 0.5 and 1)%wt., are deposited on glass substrates by pulsed laser deposition (PLD) technique for study characterization ZnO:Fe2O3 as solar cell electrode. The profound effect of mixed film on the structural and optical of ZnO: Fe2O3 thin films was observed. Meanwhile, the films have polycrystalline Hexagonal structures for ZnO, Rhombohedra and cubic structure for Fe2O3, and as indicated by the X-ray diffraction patterns of the films. The mean crystallite size of ZnO increase with increasing mixed ratio. The direct energy gap (Eg) of ZnO is 3.36 eV and decreasing with increasing mixed ratio.

Surface plasmon resonance could increase the efficiency of solar cells , when light is trapped by the noble metallic nanoparticles arrangement at and into the silicon solar cell (SSC) surface. Pure noble metal (silver and gold) nanoparticles (NPs) have been synthesized as colloids in de-ionized water (DW) by pulsed laser ablation (PLA) process at optimum laser fluence. Silicon solar cell with low efficiency was converted to plasmonic silicon solar cell by overcasting deposition method of silver nanoparticles on the front side of the SSC. The performance of plasmonic solar cell (PSC) was increased due to light trapping. Two mechanisms were involved : inserting silver nanoparticles (Ag NPs) inside the silicon layer by the heating effect of pulsed laser and depositing gold nanoparticles (Au NPs) on the surface of the SSC by overcasting method. The optical properties of silver and gold colloidal solutions were studied with UV- Visible spectrophotometer with a range from 190 nm to 1100 nm. The absorption spectra showed single absorption peak located at about the characteristic value for silver and gold nanoparticles due to the surface plasmon resonance. Atomic Force Microscope (AFM) images were studied , the ablated noble NPs by pulsed laser have an average diameter less than 100 nm. AFM images showed the morphology of SSC surface without and with nanoparticles before and after overcasting and heating by laser methods. Electrical measurements for SSC namely current – voltage ( I-V )characteristics and responsivity (Rλ) displayed higher efficiency after these procedures. The efficiency rise to(5.2%) due to the localized surface plasmons excitation of (Ag NPs) that were embedded into the silicon layer by the heating effect of pulsed laser. The deposition of AuNPs on the silicon surface of the plasmonic SC additionally increased the efficiency to (7.28%), due to light trapping by scattering from Au NPs towards the plasmonic solar cell depth .

In this paper, the productions of gallium oxide (Ga2O3) nanoparticles were achieved via using the Nd: YAG laser deposition method with a fundamental wavelength (1064 nm). These nanoparticles were characterized by using different methods such as X-ray diffractometer (XRD), atomic force microscopy (AFM) and Ultraviolet–visible (UV–vis) spectroscopy. To examine the effects of laser energy on the properties of nanoparticles, the experimental results and theoretical considerations were prepared by the effective method of pulse laser deposition. The synthesis of Ga2O3NPs) was achieved with different ranges of energies (500 to 900 mJ). Average crystallite sizes of the synthesized nanoparticles were found to be in the range of 15-37 nm. On the other hand, the AFM images showed that the size is ranging between 60 and 85 nm. Optical parameters of the samples showed a strong dependence on average crystallite size.