Integrated optics demand waveguides on Si platforms with different funtionalities and thus thin film technologies become essential tools for its development. Incorporating rare-earth ions or metal nanoparticales in dielectric hosts are respectively of interest for producing active media for gain devices or non-linear optical media with a high potential for all-optical switching. In this work, pulsed laser deposition is used to produce these materials with "dopant" distributions controlled within the nanometre scale embedded in a deilectric host. Examples will be given in which the control of this distribution is essential for achieving optimised optical transmission, propagation losses or photoluminescence lifetime. These examples are additionally used to show that controlling the separation between "dopants" becomes a useful tool to provide new insights in the understanding of interaction mechanisms.
In this work, pulsed laser deposition has been used to produce Er3+ doped lead-niobium-germanate thin films from Er3+ doped 50Geo2-25PbO-25Nb2O5 transparent glasses with an Er2O3 content in the 0.5-3 weight % range. In all cases, by pumping the 4I11/2 level of Er3+, the as deposited films are optically active showing at room temperature the 4I13/2 →4I15/2 emission centered around 1530 nm. The luminescence intensity increases as the Er3+ content in the targets increases, whereas the opposite behavior is observed for the luminescence lifetime. The emission intensity and lifetimes of the 1.5 μm emission increase upon annealing.
The cleaning of silicon surfaces from submicron dust particles has been studied by means of the 'Steam Laser Cleaning' (SLC) process and compared to 'Dry Laser Cleaning' (DLC) which is used nowadays in many applications. For SLC a thin liquid layer (e.g. a water- alcohol mixture) is condensed onto the substrate, and is subsequently evaporated by irradiating the surface with a short laser pulse. The DLC process, on the other hand, only relies on the laser pulse, without application of a vapor jet. We have systematically investigated the efficiency of these two processes for the removal of well-characterized polymer, silica and alumina particles of various sizes down to 60 nm in diameter, and have also studied the influence of light wavelength and laser pulse duration for nanosecond and picosecond pulses. The results demonstrate that for the gentle cleaning of silicon wafers SLC is a very efficient method and is superior to DLC. An effect which so far has only rarely been taken into account for laser cleaning is the field enhancement under the particles, which can give rise to serious surface damage, in particular when cleaning pulses in the picosecond and femtosecond range in the DLC are applied.
The present study concerns the cleaning of materials using pulsed laser irradiation and it summarizes the most recent results obtained by the collaborative research of different European groups, within the framework of a European program for training and mobility of researchers. A series of pulsed lasers, which emit at various wavelengths (from UV to IR) with short duration of pulse (few nano-, pico- or femto- seconds), is used for the removal of metallic, ceramic and organic pollutants from contaminated solid surfaces of different natures. The scientific results obtained so far are focused on the laser cleaning of silicon wafers from sub-micrometer particles, the theoretical modeling of particles removal mechanism during dry laser cleaning, the removal of oxide layers from oxidized metals and alloys, as well as on the development of laser imaging as a diagnostic tool for the estimation of the efficiency of the proposed cleaning technique.
Nanocomposite thin films formed by metal or semiconductor nanocrystal (NCs) embedded in a host exhibit interesting nonlinear optical properties relate to the small size of the NCs. These properties make these materials potential candidates for the development of all-optical switching devices. The challenge is to produce nanocomposite materials with controlled and suitable characteristics. The present work aims to show that nanocomposite materials produced by pulsed laser deposition (PLD) might have superior structural and non-linear optical properties than those obtained by other techniques. This result will be illustrated in systems formed by metallic NCs embedded in an Al2O3 host. Fundamental aspects related to the nucleation and growth mechanisms or the reactivity of the NCs with the host will be discussed. Finally, the excellent nonlinear properties of the PLD synthesized composites will be illustrated in the case of Cu:Al2O3 films, in which the dependence of the nonlinear third order optical susceptibility has been investigated as a function of the NCs size and (chi) (3) values as large as 10-7 esu have been achieved.
This paper presents recent results on the synthesis by pulsed laser deposition (PLD) and optical properties of composite thin films consisting of metallic nanocrystals embedded in an amorphous host. The films are grown by alternate ablation of the metal and host targets in vacuum by means of an ArF laser. The results show that PLD is a very promising technique for producing these materials with nanocrystals of controlled size and in-depth distribution. The analysis of the structure of the films as a function of the number of laser pulses in the metal target allow us to discuss the nanocrystals growth mechanism. A survey of works reporting the synthesis of similar films with metallic nanocrystals embedded in an insulator host and exhibiting third order optical nonlinearities is included, which evidences that the films grown by PLD have excellent properties for waveguide applications.
Integrated optical lasers and amplifiers are attracting large attention for their use in optical sensing as well in optical communication systems. Here we present preliminary results on the characterisation of optical waveguides fabricated in Er- doped phosphate glasses either by ion-exchange or by pulsed laser deposition. It is shown that spectroscopic features of the waveguides are fully suitable to the implementation of active guided-wave devices.
Richard Haglund, Carmen Afonso Rodriguez, Giancarlo Battaglin, Mukund Godbole, Francesco Gonella, John Hamilton, Douglas Lowndes, Robert Magruder, Paolo Mazzoldi, Dannie Osborne, J. Solis
Nonlinear optical materials comprising metal nanocrystallites embedded in linear and nonlinear dielectrics are of wide current interest for use in all-optical switching devices. We have investigated several ways in which laser- and ion-beam processing can be used to create vertically and/or laterally patterned nanostructured composite materials. Pulsed laser deposition using both metal and dielectric targets can be used to create layered structures in which some layers contain quantum dots as a nonlinear element. Ion beams can also be used to induce the formation of deep waveguides in soda-lime glass subjected first to Ag ion exchange. When these Ag quantum-dot composites are irradiated by high-intensity laser light, a photochemical reaction generates Ag2O nanoclusters, changing the sign of the nonlinear index of refraction. This phenomenon offers unusual possibilities for spatially modulating a nonlinear waveguide with very high lateral resolution. Finally, we consider the use of lasers in conjunction with laser- or particle-beam-created surface defects to serve as distributed nucleation sites for quantum- dot growth. Atomic-force microscopy on planar versus offcut surfaces shows that substrate orientation, temperature and deposition pressure can be used to control the size distribution and two-dimensional growth pattern of Au nanoclusters on strontium titanate substrates.
Time and space resolved optical measurements of the laser induced
plasma emission have been performed during the growth of Ge films in
vacuum (105 mbar) and in an oxygen partial pressure up to 103 mbar. From
these irteasurements,the tiite of flight spatial distribution of the
plasma species as well as their average velocity is stablished. The
velocity is found to be 3x106 cm/s and is not influenced by the presence
of oxygen in the studied pressures interval. The lack of differences in
the plasma behavior when ablation takes place in vacuum or in oxygen
pressure is consistent with the low oxygen content found in the films.
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