We present a review of our recent research on the use of photonic crystal fibers (PCFs) to manipulate the
propagation of ultrashort pulses. The combination of a high nonlinear coefficient and unusual wavelength-dependent
group-velocity-dispersion "landscapes", together with the ability to taper the properties along the
fiber by thermal post-processing, allows observation of many interesting effects. These include generation
of THz trains of equidistant sub-50 fs pulses, highly efficient supercontinuum generation from the UV to
the IR, soliton collisions and observation for the first time of a soliton blue-shift, counteracting the Raman-related
soliton self-frequency shift.
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<sup>+</sup> 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 ≈ 600<sup>o</sup>C 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
Glass containing spherical silver nanoparticles shows a strong extinction band in the visible range due to the surface plasmon resonance (SPR) of the particles. Irradiating this material with intense, ultrashort laser pulses with a wavelength close to the SPR leads to permanent changes of its optical properties. In particular, using linearly polarized pulses, we observed strong dichroism; the latter is nanoscopically caused by deformation of the particles to ellipsoidal shapes with an additional halo of small silver particles around the central one, with a preferential orientation. In case of a single laser shot of sufficient intensity this orientation is orthogonal to the laser polarization, whereas multi-shot irradiation usually causes preferential orientation along the laser polarization. This effect is quite useful for the production of dichroitic or polarizing microstructures, and optical elements or optoelectronic devices. In this paper we describe the results of a variety of experimental studies (mostly femtosecond laser pump-probe, electron microscopy, photoluminescence) on the understanding of the physical processes, which show clearly that ultrafast ejection of electron and silver ions into the glass matrix is the starting mechanism, whereas in the course of deformation diffusion processes controlled by the local temperature play a decisive role for the final particle shapes (and thus the optical properties after laser treatment).
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.