Laser-processing the inner surfaces of 15 m long vacuum pipes installed in the LHC aims to create a nanostructured functional surface with low Secondary Electron Yield (SEY). The experimental system to treat the vacuum pipes in-situ, including a 532 nm picosecond-laser, a 15 m long optical fiber, and an inchworm robot, will be presented. The laser-induced generation of micro- and nanostructures reduces the SEY of the surface. To optimize the surface treatment, the processing parameters were varied, and different scanning patterns applied. The variation in ablation depth, surface topography and composition correlate well with changes of the SEY.
A simple technique to prepare large-area, regular microstructures in glass containing silver nanoparticles is presented. Here the modification of spatial distribution of the nanoparticles is achieved using a direct current (DC) electric field at moderately elevated temperatures. The technique exploits the recently reported effect of "electric field-assisted dissolution" (EFAD) of silver nanoparticles during which the silver nanoparticles embedded in a glass matrix can be destroyed and dissolved in the glass in form of Ag+ ions by a combination of an intense DC electric field (~1kV) and moderately elevated temperature (~280°C). This process can lead to a total transparency of the nanocomposite glasses, which to our knowledge can not be achieved via any other technique.
In this work, the possibility to produce orderly-oriented array of embedded, 2-D, micron size optical structures in silver-doped nanocomposite glass is demonstrated. This could lead to an easy way for production of many useful optical devices based on the composite materials.
By irradiating glass containing spherical Ag nanoparticles successively with fs laser pulses at different wavelengths, we were able to produce three-dimensional, permanent anisotropic modifications based on shape deformations of the nanoparticles in this nanocomposite material. This novel method is able to create dichroism in the visible and near IR part of the spectrum by deformation of nanoparticles to oblong shapes oriented parallel to the laser polarization. Using samples with a vertical gradient of the fill factor of Ag nanoparticles in the glass substrate and an accordingly inhomogeneous broadening of the surface plasmon band, modifications in various depths can be made using different excitation wavelengths. The induced modifications are reversible: heating to ≈ 600oC restores the spherical shape of Ag nanoparticles. This technique can be useful for manufacturing of different, 3D, polarization and wavelength selective micro-devices such as polarizers, filters, gratings, display and rewriting optical 3D data storage devices. As examples, we will demonstrate in this paper how (i) three areas of different color can be produced in three different depths of the sample and (ii) how a series of multicolor irradiations can be used to produce dichroic structures of high polarization
contrast.
We study different effective medium theories for describing the optical behaviour of composites consisting of spherical metallic inclusions embedded in a dielectric matrix. The analysis is performed according to the Bergman spectral density theory. This theory establishes that any effective medium model has an integral representation in terms of a function (the spectral density) that depends on the geometry of the two-phase mixture and is independent of the optical constants of the composing materials. We review classical effective medium theories (Maxwell-Garnett and Bruggeman models) according to their spectral density. Furthermore, numerical simulations based in recent works allow studying the influence of different geometric parameters in the spectral density and compare the results with the classical theories.
Here we report, for the first time to our knowledge, a cladding-pumped passively Q-switched Er-Yb codoped fiber laser with Cr2+:ZnSe and Co2+:MgAl2O4 as saturable absorbers. The maximum average output power for both crystals was 1.4 W, with typical pulse energy was 20 μJ corresponding to 60 W peak power. The pulse duration could be varied between 370 - 700 ns and repetition rate between 20 and 85 kHz by adjusting the pump power.
A double-clad thulium-doped silica fibre laser, pumped by two beam-shaped diode-bars operating at 787-790nm, has yielded 14W of single-mode output at ~2µm, with a slope efficiency with respect to launched power of 46%. Using a tunable laser configuration, comprising an external cavity with a diffraction grating, a maximum output power of 10.5W at 1921nm has been obtained, and wavelength tuning at multi-watt power levels over 215nm from 1855 to 2070nm has been demonstrated. The prospects for further improvement in performance will be discussed. In addition, a simple approach for further scaling of power levels from fibre lasers in the two-micron regime, based on intracavity wavelength combining of multiple fibre lasers is described. In a preliminary demonstration, four cladding-pumped thulium-doped silica fibre lasers are wavelength-combined yielding an output power >14W. The prospects for further increase in output power via this approach will be discussed.
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