Philippe Delaporte

ABSTRACT Laser near-field enhancements underneath transparent microspheres can be used to locally implement new functionalities in materials. Using this technique, we report micro- and nano-structuration on silicon (Si). The Langmuir-Blodgett (LB) technique is primarily used to realize monolayers of C18 functionalized silica (SiO2) microspheres on a large size area of the substrates. Afterwards, by irradiating the deposited monolayer with single shot UV nanosecond laser pulses in the ablation regime, we demonstrate the formation of dense arrays of craters in silicon substrate. In particular, we describe our works to obtain mono dispersed craters of sub micrometer size using LB technique and taking the fluence and sphere size as variable process parameters. Finite-difference time-domain (FDTD) simulations are presented to estimate the enhancement intensity factor and near-field distribution below the spheres in the experiments.

"The use of laser technology for cleaning heritage artefacts is gaining increasing interest both in Australia and overseas. Laser cleaning is a dry and contact-free process, which selectively removes contaminating dirt or coatings (including hazardous contaminants such as radioactivity and biological material), minimises mechanical and chemical disruption of historic surfaces and generates minimal waste. However, the disadvantage of current lasers for conservation is that their relatively long pulse duration allows heat and shock waves to travel into the substrate, potentially causing damage to historic surfaces. Different laser types are also needed to treat different materials, which limits the range of materials any one laser unit can treat. The femtosecond pulses used by ultrafast lasers however, are too short to allow heat or shock waves to travel into the substrate. They ablate very thin surface layers through a process known as non-thermal or non-equilibrium laser ablation. This allows highly controlled cleaning, does not affect the substrate material, and can be combined with real-time monitoring with a system such as Laser-Induced Breakdown Spectroscopy to analyse the ablated products and prevent damage to uncontaminated layers under the surface of an object. This paper describes the differences between conventional and ultrafast lasers, and outlines the aims of a new Australia Research Council project to develop the ultrafast laser technique for conservation"

During the wheat milling process, the bran fractionation is related to its mechanical properties, which are measured using tensile tests on hand-isolated tissues. However, the dissection of wheat tissues implies a soaking stage in water that can modify tissue properties. New methodologies are required to evaluate wheat tissue properties directly on native grains. The aim of this work was to

Controlling the preparation of nano/microsphere monolayers on large areas remains a difficult task but is crucial for several fabrication methods of highly-ordered periodic nanostructures. We demonstrate the preparation of ordered monolayers of few square centimeters with an extremely high coverage ratio (>98%) by implementing a modified protocol (MP) Langmuir Blodgett (LB) technique. We use octadecyl type hydrocarbon (C18) functionalized spherical particles (polystyrene and silica) with diameters in the range 1-5μm, and a selected mixture of solvents for accurate control of the surface tension and particles' mobility at the water surface. This leads to a delicate growth of crystal-like monolayers which are subsequently transferred to glass or silicon substrates. While operating the Langmuir-Blodgett trough, a key enabling the quality enhancement resides not only on surface tension measurements but also on simple visual inspections of the water surface supporting the monolaye...

ABSTRACT Laser-matter interaction is a unique and simple approach to structure materials or locally modify their properties at the micro and nanoscale level. Playing with the pulse duration and the laser wavelength, a broad range of materials and applications can be addressed. Direct irradiation of surfaces with laser beam through a standard optical beam setup allows an easy and fast structuring of these surfaces in the range of few micrometers. However, the irradiation of materials through an array of dielectric nanospheres provides a unique opportunity to break the diffraction limit and to realize structures in the range of hundred of nanometers. This simple, fast and low-cost near-field nanolithography technique is presented and discussed, as well as its great potential. The theoretical aspects of the near-field enhancement effects underneath the particles have been studied with a simple model based on the Mie theory. A commercial FDTD software has also been used to study the influence of the substrate and the surrounding media, on the energy profile of the photonic jet generated under the sphere. A specific study has been dedicated to the influence of the dispersion of the sphere diameter on the morphology of the ablation craters. This technique has been used for patterning bi-layer substrates. The process leads to the formation of a nanoporous membrane which has been used to realize an array of gold nanodots on silicon. We have also associated the Laser-Induced Forward Transfer (LIFT) process with the near-field nanolithography to print, in a single laser shot, an array of metallic nanobumps.

Thin films of Y1Ba2Cu3O7-x were deposited via pulsed laser ablation onto MgO and YSZ (Yttria-Stabilized Zirconia) substrates. The use of an IR Nd:YAG laser leads to nonstoichiometric deposition. The best quality superconducting films were deposited by means of UV excimer laser ablation ((lambda) equals 308 nm). These films were strongly orientated with c-axis perpendicular to (100) substrate. The film quality was found to be strongly dependent on substrate temperature, oxygen pressure, sample cooling rate and laser fluence. The deposition process was characterized by the time-resolved spectroscopic measurements of the emission from YO molecules.

The uniformity and stability of discharge process in a high pulse repetition frequency (PRF) long pulse XeCl laser are investigated for three different electrode materials (aluminum, copper, brass) and different roughnesses of the copper electrode versus PRF (f less than or equal to 700 Hz) for burst durations of 10 shots. The discharge quality evolution is experimentally analyzed from discharge photographs obtained with a CCD video camera and pressure perturbation measurements achieved with a piezoelectric pressure probe placed very close to the discharge volume.

Transmission of XeCl excimer laser pulses through commercial silica optical fibers with high OH content have been investigated. The Ultraviolet irradiation of these optical fibers includes color center generation and two photon absorption in the fiber core. These absorbing centers disappear at room temperature. A spectroscopic study of fiber core fluorescence permitted to clearly identify the Non Bridging Oxygen Hole

Alkali rare gas triatomic ionic excimers have been observed for the first time. These molecules have been produced by electron beam excitation of rare gas alkali mixtures at high pressure and high temperature. Emission spectra centered at approximately 159 nm have been observed and attributed to Kr2+Cs ions. Lifetimes and binding energies of the lowest excited states have been estimated.

The uniformity and stability of discharge process in a high pulse repetition frequency long pulse XeCl laser are investigated for three different copper electrode roughnesses in single shot regime and versus PRF. The discharge quality evolution is experimentally analyzed from discharge photographs obtained with CCD video camera and pressure perturbation measurements achieved with a piezoelectric pressure probe placed very close to the discharge volume.

... oscillator: regenerative-amplifier excimer laser system. [Proceedings of SPIE 3574, 36 (1998)]. Olivier P. Uteza, Philippe C. Delaporte, Bernard L. Fontaine, Marc L. Sentis, Stephane Branly, Maxim K. Makarov, Michel Pealat. Abstract. ...