Hydrodynamic simulations of metal ablation by femtosecond laser irradiation

Ablation of Cu and Al targets has been performed with 170 fs laser pulses in the intensity range of 10^12-10^14 W/cm^2. We compare the measured removal depth with 1D hydrodynamic simulations. The electron-ion temperature decoupling is taken into account using the standard "two-temperature model". The influence of the early heat transfer by electronic thermal conduction on hydrodynamic material expansion and mechanical behavior is investigated. A good agreement between experimental and numerical matter ablation rates shows the importance of including solid-to-vapor evolution of the metal in the current modeling of the laser matter interaction

Comparison of Heat Affected Zone due to nanosecond and femtosecond laser pulses using Transmission Electronic Microscopy

International audienceThis letter presents a method aimed at quantifying the dimensions of the heat-affected zone ~HAZ!, produced during nanosecond and femtosecond laser–matter interactions. According to this method, 0.1 mm thick Al samples were microdrilled and observed by a transmission electronic microscopy technique. The holes were produced at laser fluences above the ablation threshold in both nanosecond and femtosecond regimes ~i.e., 5 and 2 J/cm2, respectively!. The grain size in the samples was observed near the microholes. The main conclusion is that a 40 mm wide HAZ is induced by the nanosecond pulses, whereas the femtosecond regime does not produce any observable HAZ. It turns out that the width of the femtosecond HAZ is less than 2 mm, which is our observation limit

Integrated optical transfection system using a microlens fiber combined with microfluidic gene delivery

Optical transfection is a promising technique for the delivery of foreign genetic material into cells by transiently changing the permeability of the cell membrane. Of the different optical light sources that have been used, femtosecond laser based transfection has been one of the most effective methods for optical transfection which is generally implemented using a free space bulk optical setup. In conventional optical transfection methods the foreign genetic material to be transfected is homogenously mixed in the medium. Here we report the first realization of an integrated optical transfection system which can achieve transfection along with localized drug delivery by combining a microlens fiber based optical transfection system with a micro-capillary based microfluidic system. A fiber based illumination system is also incorporated in the system in order to achieve visual identification of the cell boundaries during transfection. A novel fabrication method is devised to obtain easy and inexpensive fabrication of microlensed fibers, which can be used for femtosecond optical transfection. This fabrication method offers the flexibility to fabricate a microlens which can focus ultra-short laser pulses at a near infrared wavelength to a small focal spot (~3 µm) whilst keeping a relatively large working distance (~20 µm). The transfection efficiency of the integrated system with localized plasmid DNA delivery, is approximately 50%, and is therefore comparable to that of a standard free space transfection system. Also the use of integrated system for localized gene delivery resulted in a reduction of the required amount of DNA for transfection. The miniaturized, integrated design opens a range of exciting experimental possibilities, including the dosing of tissue slices, targeted drug delivery, and targeted gene therapy in vivo

Multiphoton excitation of surface plasmon-polaritons and scaling of nanoripple formation in large bandgap materials

We report studies of multiphoton mechanisms of plasmon excitation and their influence on the femtosecond-laser induced subwavelength ripple generation in large-bandgap dielectric and semiconducting transparent materials. An extended Drude Sipe formalism is applied to quantitatively estimate the real part of the dielectric function which is dependent on the carrier density. The theory is able to predict the ripple periods for selected materials in good agreement with the experimental observations. Possible limitations at very small spatial periods are also discussed

Development of a versatile two-photon endoscope for biological imaging

We describe a versatile, catheter-type two-photon probe, designed for in vivo and ex vivo imaging of the aqueous outflow pathway in the eye. The device consists of a silica double cladding fiber used for laser delivery and fluorescence collection, a spiral fiber scanner driven by a miniature piezoelectric tube, and an assembly of three micro-size doublet achromatic lenses used for focusing the laser and collecting the two-photon excitation signal. All the components have a maximum diameter of 2 mm and are enclosed in a length of 12-gauge stainless steel hypodermic tubing having an outer diameter of 2.8 mm. The lateral and axial resolutions of the probe are measured to be 1.5 μm and 9.2 μm, respectively. Different lens configurations and fibers are evaluated by comparing their spatial resolutions and fluorescence signal collection efficiencies. Doublet achromatic lenses and a double cladding fiber with a high inner cladding numerical aperture are found to produce a high signal collection efficiency, which is essential for imaging live tissues. Simple methods for reducing image distortions are demonstrated. Images of human trabecular meshwork tissue are successfully obtained with this miniature two-photon microscope

Optical 3D-storage in sol-gel materials with a reading by Optical Coherence Tomography-technique

We report on the recording of 3D optical memories in sol-gel materials by using a non-linear absorption effect. This effect induces a local change of the optical properties of the material which is read and quantified with a high resolution full-field Optical Coherence Tomography setup. It is the first time that this technique is used for this purpose. Data recording was performed by focused picosecond (ps) single-pulse irradiation at 1064 nm with energy densities of 10 and 33 J/cm2 per pulse.Comment: 19 pages, 7 figure

Interaction of ultrafast laser pulses with nanostructure surfaces

The interaction of ultrafast laser pulses with surfaces on the nanoscale paves the way for various innovative technologies in spectroscopy, photovoltaics, photocatalysis, or medicine, to mention only a few. The basic mechanisms, however, are still the subject of intense research. We take a closer look at this topic from different viewpoints. The first aspect is the enhancement of the efficiency of physical or chemical processes by producing local field maxima and resonances at top-down or bottom-up structured surfaces. A further aspect is the dynamic change of optical properties by inducing free carriers and plasmons. Last but not least, permanent nanostructures can be obtained as a result of nano-feedback and self-organization. In high-energy laser physics, all three aspects play a role at once. Therefore, particular attention will be paid to this emerging field

Etude des procédés laser femtoseconde pour le micro-usinage à effets thermiques limités

L'ensemble des études présentées dans ce mémoire souligne le réel potentiel des lasers femtoseconde pour des applications de micro-usinage et insiste sur la maîtrise de l'utilisation des chaînes laser amplifiées. Les dispositifs expérimentaux mis en place pour contrôler l'usinage nécessitent la maîtrise de nombreux paramètres, qu'il soient mécaniques, informatiques ou optiques. Différentes techniques ont été élaborées pour accroître la qualité d'usinage et de perçage et des études systématiques ont été entreprises dans le cas des métaux sur l'effet de la fluence et de la cadence. Une comparaison des effets thermiques sur les bords d'usinage en mode femtoseconde et nanoseconde a été entreprise d'un point de vue expérimental (MET) et par l'intermédiaire d'un modèle à 2 température. Enfin des résultats plus exploratoires, en particulier sur le silicium ainsi que des essais de photoinscription de guide d'onde illustrent le potentiel applicatif considérable des impulsions ultra-courtesThe studies presented in this thesis underline the real potential of femtosecond lasers for micromachining applications and insist on the control and use of the amplified laser chains. The experimental devices for the control of micromachining require the control of many parameters, as mechanical, data-processing or optical. Various techniques of machining were worked out to increase the quality of machining and drilling and systematic studies were undertaken in the case of metals including fluence and repetition rate dependence. A comparison of the heating effects on the edges of holes drilled in femtosecond and nanosecond regime was performed with an experimental approach (TTM measurements) and with a modelization. This was based on the use of a 2 temperatures model. Finally complementary results, in particular on silicon micromachining and tests of wave guide photowritting illustrate the wide applicability field of the ultra-short laser pulsesST ETIENNE-BU Sciences (422182103) / SudocSudocFranceF

Le français régional de la région de Morlaix, Basse-Bretagne (enracinement sociolinguistique et fonctionnements)

What does the expression 'breton accent' often heard in Low Brittany mean? In Low Brittany, french and breton, two languages of different origins had once their defined limits. For historical reasons, french has gradually spread into breton. At the beginning, the penetration was inconscious, the breton language acquired a lot of new words that described new ideas, customs and objects. Over the years, french has become the common language for Low Brittany, something that breton, with its dialectal diversification, has never been. The french introduced to Low Brittany is necessarily influenced by the breton language. The vocabulary of the spoken french in Low Brittany is not only permeated with breton words and expressions, but the breton also influences the phonology, intonation and morphology of the french in Low Brittany. Theses contacts are of course noticeable in spoken french as well as in its written literaly form. The different researches have shown that the regionalized french reveals the Breton's attachment to their local traditions and the breton language. Since the breton can no longer mark breton identity and particularity, Low Brittany's french has taken over this function and is able to distinguish the Bretons from other linguistic communities. All these issues constitute the subject of this research. The regional french in Low Brittany is analysed functionnaly and sociolinguistically. Finaly the thesis is essential to sociolinguistic studies in Brittany and also, from a human point of view, to the entire linguistic community of Low Brittany.Que représent l'expression 'accent breton', si souvent entendue en Basse-Bretagne? Le français et le breton, deux langues d'origine différente, avaient autrefois leurs limites exactes en Basse-Bretagne. Par nécessité historique, le français a progressivement envahi le breton. Au départ, cette pénétration s'est faite par une sorte d'endosmose insensible, le breton recevant sans s'en douter tout un flot de mots nouveaux, représentant des idées, des moeurs et des objets nouveaux. Au fil du temps, le français est devenu la langue commune que le breton, avec le morcellement de ses dialectes, n'a jamais été. Le français introduit en Basse-Bretagne se ressent alors inévitabllement du voisinage du breton. Le vocabulaire du français parlé en Basse-Bretagne est imprégné de mots ou d'expressions du breton. Mais le substrat exerce aussi son action sur la phonologie, l'intonation et la morphologie du français. Ces contacts se ressentent dans le français parlé mais également sous la forme littéraire écrite. Les différentes enquêtes menées ont montré que ce français régionalisé témoigne de l'attachement des Bretons à leurs traditions locales et à la langue bretonne. Si le breton ne parvient plus à marquer l'identité bretonne, le français régional en Basse-Bretagne joue aussi ce rôle de différenciation por rapport à d'autres communautés linguistiques. Toutes ces donées constituent le thème de cette recherche . Le français régional y est analysé de manière fonctionnelle et sociolinguistique. Enfin, ce travail de recherche est non seulement utile pour la recherche sociolinguistique en Basse-Bretagne, mais également d'un point de vue humain, pour l'ensemble de la communauté linguistique de Basse-Bretagne.RENNES2-BU Centrale (352382101) / SudocSudocFranceF