Search

Summarization: This study describes the fabrication of ultrafast laser-induced periodic nanostructures on Nickel sheets and their use as cathodes in alkaline electrolysis. For the first time, to the best of our knowledge, laser-nanostructured Ni sheets were used as cathode electrodes in a custom-made electrolysis cell at actual, Hydrogen producing conditions, and their efficiency has been compared to the untreated Nickel sheets. The electrochemical evaluation showed higher Jpeaks, lower overpotential, and enhanced double-layer capacitance for the nanostructured electrode. A decrease in the Tafel slope was also found for the nanostructured electrode. The hydrogen production efficiency was found to be 3.7 times larger for the laser-nanostructured Nickel electrode, which was also confirmed by current-time measurements during electrolysis. Also, a novel approach is proposed to improve the stability of the current density during electrolysis and, therefore, the hydrogen production process by about 10%. Presented on: International Journal of Hydrogen Energy

Deposition of Au nanoparticles (NPs) through UV ultra-short-pulse laser ablation in vacuum is a methodology suitable for obtaining high purity supported plasmonic NPs with a superb adherence to both planar and patterned substrates. Furthermore, the peculiarity that upon sub-picosecond laser irradiation NPs form directly within the target leads to narrow and controlled size-distribution. While extensive literature theoretically models phase changes and pressure relaxation of metal targets under sub-picosecond irradiation, the evolution of the nanostructured deposit through different ablation regimes is poorly documented experimentally. In this paper, besides modeling the temporal evolution of electron and lattice temperature following sub-picosecond laser pulse irradiation of Au bulk at the threshold ablation fluence (0.1 J/cm2), we report an accurate statistical, morphological and structural characterization of the AuNP distributions as a function of the laser fluence tuned from 0.1 to 3 J/cm2 to drive the target through two ablation regimes. The occurrence of photomechanical spallation and phase explosion at low and high fluence, respectively, is correlated with the evolution of the NP deposits, which are discussed by providing a physical insight in the interplay between fluence-driven ablation regimes of the target, arrangement kinetics of the deposited species (NPs and vapour species) and (crystalline or amorphous) phase of the NPs. This knowledge is key for controlling the surface plasmon resonance response of AuNPs depending on the designed application.

The ablation of a metal target at laser energy densities in the range of 1–10 TW/cm2 leads to the generation of nanoparticles (NP) of the ablated material. This aspect is of particular interest if the immobilization of NPs on three-dimensional (3D) substrates is necessary as for example in sensing applications. In this work the deposition of Au NP by irradiation of a Au bulk target with a sub-picosecond laser beam (500 fs; 248 nm; 10 Hz) on 2D (silica and Si(100)) and 3D substrates (silica nanowire forests) is reported for different number of laser pulses (500, 1000, 1500, 2000, 2500). A uniform coverage of small Au NPs (with a diameter of few nm) on both kinds of substrates has been obtained using a suitable number of laser pulses. The presence of spherical droplets, with a diameter ranging from tens of nm up to few μm was also detected on the substrate surface and their presence can be explained by the weak electron-phonon coupling of Au. The optical characterization of the samples on 2D and 3D substrates evidenced the surface plasmon resonance peak characteristic of the Au NPs although further improvements of the size-distribution are necessary for future applications in sensing devices.

Since the global energy demand increases annually, a great need is arising in energy-related technologies. Photocatalysis plays a major role in these technologies, as it exploits one of the renewable types of energy, solar energy. For this reason, there is a plethora of scientific investigations in the research field of photocatalysis. In particular, the variety of materials that could be employed to efficiently enhance the procedure, is extensively studied. One of the most widely used materials is titania (TiO 2 ) due to its efficiency in photocatalysis [1] , while maintaining and other notable properties such as non-toxicity, chemo-stability, enhanced electronic and optical characteristics.

The sensing properties of zinc oxide (ZnO) combined with tilted fiber Bragg gratings have been studied in this work for the development of organic vapor optical fiber sensors. ZnO has been deposited onto tilted optical fiber Bragg gratings by drop casting technique to obtain coatings with thickness below 100nm. For a title angle of 4°, cladding modes up to 4 dB peak to peak amplitude were obtained and, as a consequence, the fundamental mode strength dropped below 0.5dB. The sensing features were evaluated by exposing the sensor to saturated atmospheres of three different alcohols and acetone. A negligible change was registered for methanol but in the case of ethanol and isopropanol a 24pm red shift was observed; in the case of acetone, the shift was 96pm which is of the order of spectral width of certain cladding modes. For all cases, the shifts were reversed once the organic vapors were removed. Ongoing studies are focused on the optimization of the sensing layer as well as the tilted angle to enhance the spectral response of the sensor.

Even if it has been recently assessed that sub-picosecond ablation is not a “melting-free” process, a systematic investigation of the issue of droplets is still lacking. In this paper we discuss the effects of fluence (F = 0.3, 1, 3 J/cm 2 ), target-substrate distance (d TS = 5, 6, 7, 8, 9 cm) and number of laser pulses per site (N p/s = 2, 12, 22, 36, 96) on the morphology in terms of droplets and plasmonic response of gold nanoparticles deposited by sub-picosecond pulsed laser ablation. Among metals, gold is an ideal candidate to study the occurrence of droplets due to its low electron-phonon coupling that favors the appearance of heat affected zones. Our findings demonstrate that N p/s affects the production of large droplets more intensely than F and d TS . In fact, increasing N p/s produced much larger droplets than the ones obtained by tuning the fluence and an increment in the droplet density of 10 times. On the other hand, while the maximum density of small droplets (average diameter ≤ 0.15 μm) occurs at F = 1 J/cm 2 (with respect to 0.3 J/cm 2 and 3 J/cm 2 ), the total droplet density exhibits a minimum at such fluence.

The fabrication of nanostructures with controlled assembly and architecture is very important for the development of novel nanomaterial-based devices. We demonstrate that laser techniques coupled with low-temperature hydrothermal growth enable complex three-dimensional ZnO nanorod patterning on various types of substrates and geometries. This methodology is based on a procedure involving the 3D scaffold fabrication using Multi-Photon Lithography of a photosensitive material, followed by Zn seeded Aqueous Chemical Growth of ZnO nanorods. 3D, uniformly aligned ZnO nanorods are produced. The increase in active surface area, up to 4.4 times in the cases presented here, provides a dramatic increase in photocatalytic performance, while other applications are also proposed.

Silica two-dimensional substrates and nanowires (NWs) forests have been successfully decorated with Au nanoparticles (NPs) through laser ablation by using a pulsed ArF excimer laser, for sensor applications. A uniform coverage of both substrate surfaces with NPs has been achieved controlling the number of laser pulses. The annealing of the as-deposited particles resulted in a uniform well-defined distribution of spherical NPs with an increased average diameter up to 25 nm. The deposited samples on silica NWs forest present a very good plasmonic resonance which resulted to be very sensitive to the changes of the environment (ethanol/water solutions with increasing concentration of ethanol) allowing the detection of changes on the second decimal digit of the refractive index, demonstrating its potentiality for further biosensing functionalities.

We have ablated, for the first time, graphite in a nitrogen atmosphere at different pressures by using a sub-picosecond excimer laser (KrF, λ=248 nm, τ L =0.5 ps). In this paper, we have discussed the deposited film properties using several diagnostic techniques (scanning electron microscopy, profilometry, X-ray photoelectron spectroscopy, Fourier transform, infrared and Raman spectroscopies) in terms of the different physical mechanisms involved in the reactive laser ablation process when the graphite target is ablated in a nitrogen atmosphere by lasers with different pulse duration. The deposition rate, the nitrogen concentration and the amount of the carbon bonded to nitrogen atoms were extremely reduced with respect to what was observed in the films deposited by nanosecond lasers. Moreover, the particulate and droplet density, one of the worst drawbacks of laser deposition technique, was not decreased.

The effects of high laser fluence on the properties of CN x thin films prepared by reactive pulsed laser (KrF excimer laser, λ =248 nm, τ FWHM =30 ns) ablation at two different N 2 gas pressures were investigated. A variety of analytical techniques have been used to characterize the structure and properties of the deposited films: X-ray photoelectron spectroscopy; X-ray diffraction; scanning electron microscopy; energy dispersive X-ray spectroscopy; Fourier transform infrared; and Rutherford backscattering spectroscopy. Analysis of these data shows the existence of a certain amount of covalent C–N single bonds and a nitrogen content up to 44%. The results also show the presence of covalent C≡N triple bonds in the film deposited at high nitrogen pressure (50 Pa). Comparison with the films deposited by XeCl excimer laser ( λ =308 nm, τ FWHM =30 ns), at the same experimental conditions, will also be presented.

This study reports patterning of surfaces with Zn using the laser induced forward transfer (LIFT) technique and subsequent chemical growth of ZnO thin films. The LIFT process is performed both in vacuum and in air and yields a Zn pattern on the receiving substrate. These Zn patterns were used as precursors to chemically grown ZnO thin films, and the morphology of these films was investigated and compared. Inspection of the films grown from the in-vacuum deposited pattern revealed the aligned growth of ZnO nanorods (NRs), in the regions where the Zn precursor was deposited, while no substantial ZnO growth was observed outside the precursor patterns. The ZnO films grown from the in-air deposited patterns show different growth behaviour; the precursor pattern is not well preserved and the surface morphology reveals flower-type ZnO nanorods. The difference in morphology of the seeding Zn patterns deposited under the two environments (vacuum versus air) directly translates into different morphology ZnO features, chemically grown from these patterns (nanorod versus flower growth).

In our study we investigate and report the femtosecond pulsed laser deposition of biological and biocompatible materials. Teflon, polyhydroxybutyrate, polyglycolic-acid, pepsin and tooth in the form of pressed pellets were used as target materials. Thin layers were deposited using pulses from a femtosecond KrF excimer laser system (FWHM = 450 fs, λ = 248 nm, f = 10 Hz) at different fluences: 0.6, 0.9, 1.6, 2.2, 2.8 and 3.5 J/cm2, respectively. Potassium bromide were used as substrates for diagnostic measurements of the films on a FTIR spectrometer. The pressure in the PLD chamber was 1 × 10−3 Pa, and in the case of tooth and Teflon the substrates were heated at 250 °C. Under the optimized conditions the chemical structure of the deposited materials seemed to be largely preserved as evidenced by the corresponding IR spectra. The polyglycolic-acid films showed new spectral features indicating considerable morphological changes during PLD. Surface structure and thickness of the layers deposited on Si substrates were examined by an atomic force microscopy (AFM) and a surface profilometer. An empirical model has been elaborated for the description of the femtosecond PLD process. According to this the laser photons are absorbed in the surface layer of target resulting in chemical dissociation of molecules. The fast decomposition causes explosion-like gas expansion generating recoil forces which can tear off and accelerate solid particles. These grains containing target molecules without any chemical damages are ejected from the target and deposited onto the substrate forming a thin layer.

We report a method for micropatterning (25–900 μm2 pixel size) of ZnO nanorods onto a silicon substrate via a low-temperature (overall under 100 °C) two-step process, involving a laser-based direct-write technique (laser-induced forward transfer) and sequential chemical growth. The rods produced via this route are aligned in the [0001] crystal direction. Photoluminescence shows, next to the band-gap emission, strong green-yellow emission centred at ∼570 nm. Additionally, the rod arrays show excellent field-emission properties with a threshold field for emission of 5 V/μm.

Pb thin films were deposited on Nb substrates by means of pulsed laser deposition (PLD) with UV radiation (248 nm), in two different ablation regimes: picosecond (5 ps) and subpicosecond (0.5 ps). Granular films with grain size on the micron scale have been obtained, with no evidence of large droplet formation. All films presented a polycrystalline character with preferential orientation along the (111) crystalline planes. A maximum quantum efficiency (QE) of $7.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ (at 266 nm and 7 ns pulse duration) was measured, after laser cleaning, demonstrating good photoemission performance for Pb thin films deposited by ultrashort PLD. Moreover, Pb thin film photocathodes have maintained their QE for days, providing excellent chemical stability and durability. These results suggest that Pb thin films deposited on Nb by ultrashort PLD are a noteworthy alternative for the fabrication of photocathodes for superconductive radio-frequency electron guns. Finally, a comparison with the characteristics of Pb films prepared by ns PLD is illustrated and discussed.

A 248 nm (KrF) excimer laser with a repetition rate of 10 Hz, pulse duration of 30 ns and beam energy up to 450 mJ was employed to form vias in 4H-SiC substrates and Lely platelets. SEM micrographs have been used to evaluate etched material quality as well as etch rate. The area surrounding the via-holes is covered by nanoparticles, which are debris from the laser ablation and are removed by chemical cleaning and agitation. The etch-rate exhibits a perfect linear behaviour versus the number of laser pulses showing the possibility of an all-laser via-hole formation. A slight tapering along the via-holes, useful for the subsequent metallization process is also observed. Finally, a defective,15 μm wide, zone is formed nearby the sidewalls.

Pulse shaping introduces the method that makes possible the production of tunable arbitrary shaped pulses. We extend this method to control the prevalent growth of cubic SiC films on Si (1 0 0) substrates by pulsed laser deposition at temperatures around 973 K from a SiC target in vacuum. We used a laser system generating 200 fs pulses duration at 800 nm with 600 μJ at 1 kHz. The obtained structures are investigated by electron microscopy, X-ray diffraction and profilometry. We observed grains embedded in an amorphous texture, characteristic in our opinion to the depositions obtained with very short pulses. We present a comparison of deposited films with and without pulse shaping. Pulse shaping promotes increased crystallization and results in the deposition of thin structures of cubic SiC with a strongly reduced density of particulates, under similar deposition conditions.

In this paper we present the growth of La0.5Sr0.5CoO3 (LSCO) films on MgO, quartz, and silicon substrates by pulsed laser deposition (PLD) using a Ti : sapphire laser (50 fs, 800 nm wavelength). The morphology and the structure of the films were studied by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. The films were polycrystalline and exhibit a good adherence to the Si substrate. Different deposition parameters such as substrate temperature, oxygen pressure, and laser fluence were varied to achieve good surface quality and low resistivity crystalline films. We also defined the optimum conditions in which the deposited film surface is particulate free. The best films (droplets free) were grown at 625 °C, in an ambient oxygen pressure of 6 mbar, with an incident laser fluence of 0.19 J/cm2. This is a mandatory step in the complex work of fabricating La0.5Sr0.5CoO3/BaTiO3/La0.5Sr0.5CoO3 heterostructures for the development of thin film capacitors for non-volatile ferroelectric access memory devices.

Thin YAG (Y3Al5O12) and YAP (YAlO3) films doped with Er content were grown by sub-picosecond (450 fs) KrF laser deposition from crystalline Er: YAG and Er: YAP laser rods. The influence of laser power density, substrate temperature, target- substrate distance and deposition ambient atmosphere (vacuum or oxygen) was studied. Results of morphological, compositional, structural and luminescence analysis are presented. Crystalline films have been obtained even for low substrate temperature. Luminescence corresponding to Er+3 ions was observed for all the samples.

Aluminum nitride thin films were deposited by multipulse KrF* (λ = 248 nm, τ∼450 fs) excimer laser ablation of AlN targets in low-pressure nitrogen. We investigated the morphology of the deposited films by scanning as well as transmission electron microscopy, as a function of laser fluence and ambient nitrogen pressure. The AlN films entirely consist of grains (clusters) with average diameters of a few tens of nanometers. In addition, particulates several hundreds of nanometers in diameter (spherical droplets) were observed on the surfaces of the deposited films. Besides these particulates, we noticed the presence of micrometer-size whiskers, or dendritic- and wave-like structures, consisting of agglomerates of nanoparticles. The particulates density decreases with the decrease of the laser fluence, or with the increase of the ambient nitrogen pressure, while their average size increases. This indicates that clustering is the dominant particulates formation mechanism, as a result of the enhanced number of collisions in the fs laser generated ablation plasma.

We performed a comparative study of the plasma generated from AlN targets under sub-ps vs ns UV (λ=248 nm) excimer laser pulses. Optical emission and time-of-flight spectra recorded in cases of samples irradiated with ns laser pulses showed the presence of Al lines, which became prevalent after the first laser pulse was incident on the target. These observations are congruent with the metallization of AlN targets inside each crater under multipulse ns laser action at laser fluences above the ablation threshold, observed by visual inspection and optical microscopy. Metallization was not observed when working with sub-ps laser pulses. Moreover, our studies confirmed the predominant presence of AlN positive molecular ions in the plasma generated in front of AlN targets submitted to sub-ps multipulse laser irradiation. The optical emission data are in good agreement with time-of-flight mass analysis. We emphasize that all investigations support the experimental evidence reported by Gyorgy et al. [E. Gyorgy et...

Thin films of Er:YAG and Er:YAP were deposited by subpicosecond (450 fs) and nanosecond (20 ns) KrF laser (λ=248 nm) on YAG, YAP, fused silica, silicon and sapphire substrates. Laser spot size, energy density, substrate temperature and deposition ambient (vacuum and oxygen) were varied. Comparison of growth rate, morphology, composition, crystallinity and adhesion of the films grown by subpicosecond and nanosecond deposition is presented.

We investigated the relative merits and limits of pulsed laser deposition from AlN targets in vacuum and low-pressure nitrogen in obtaining stoichiometric and crystalline aluminum nitride thin films. We used two UV excimer laser sources (λ=248 nm): a nanosecond system (τFWHM=30 ns) and, a subpicosecond (τFWHM=450 fs) system. The obtained structures were characterized by x-ray diffraction, electron microscopy in cross section, selected area electron diffraction, and profilometry. We demonstrated that the best results are obtained with the sub-ps laser source in vacuum and in low pressure nitrogen when the AlN thin films are very pure, crystalline, clearly exhibiting a tendency to epitaxy. Metallic Al is present in the films deposited with the ns laser source. We believe this is an effect of the gradual decomposition of AlN inside the crater on the target surface under multipulse laser irradiation.

The angular distribution of the ablated material was studied during sub-ps Si laser ablation deposition using a special hemicylindrical substrate holder and different laser fluences ranging between 0.4 and 1.7 J/cm(2). Scanning electron microscopy analysis of the deposited films showed that, independent of the fluence, the distribution of the deposited droplets presents two maxima. The first maximum corresponds to the average plume deflection angle value due to the local surface orientation produced by the preferential etching process. The second maximum is observed approximately at 45 degrees with respect to the normal of the target surface, and is related to the phase explosion products that expand along the incident laser beam direction. The investigation of the twofold distribution of the sub-mu m size deposited droplets is important to improve the quality of the deposited coatings.

For the first time the plume deflection effect during the irradiation of silicon target with sub-ps KrF laser pulses was investigated. The morphological changes of the laser ablated target and the corresponding plume deflection angle have been studied in vacuum with different laser fluences and number of pulses. In accordance with earlier results obtained by nanosecond laser, we found a strong correlation between the morphological changes on the irradiated target and the observed plume deflection angle. As the number of laser pulses increases, the formation of well-defined silicon columnar microstructures oriented towards the laser beam has been observed on the targets ablated with fluences between 0.1 and 1.7 J/cm2 (2.2 × 1011 and 37.4 × 1011 W/cm2 of power density, respectively). It has also been observed that the plume deflection effect is present for laser fluences between 0.1 and 1.2 J/cm2, with a maximum deflection angle always higher than 20°. Simultaneously, an array of silicon substrates placed on a hemi-cylindrical holder was used for deposition experiments, in order to study the influence of the plume deflection on the thickness distribution profile of the deposited films. Profilometric analyses of the deposited silicon films revealed a non-uniform material deposition. Comparison with the results obtained by nanosecond lasers is reported and discussed.

Sharp optical fiber tips for photon scanning tunneling microscopes (PSTMs) have been fabricated by employing a new alternative technique for etching multimode optical fibers. The tip diameter is less than 30 mm, while the cone full-angle can be as sharp as 3/spl deg/. To the knowledge of the authors, such tips are the sharpest reported up to now. Measurements, with 19 tips, of the evanescent wave decay distance produced by frustrated reflection of light on a same sample, show good reproducibility. Furthermore, the PSTM images, taken with the new tips, are very sharp and fit with images of the same sample obtained with an atomic force microscope (AFM).

AlN thin films with a thickness in the nanometer range were prepared by pulsed laser deposition technique. We investigated the effect of laser wavelength, pulse duration, and ambient gas pressure on the composition and morphology of the deposited films. In all experiments we used AlN targets. We worked with three laser sources generating pulses of 34 ns@248 nm (source A), 450 fs@248 nm (source B), and 50 fs@800 nm (source C). XRD, SEM, and profilometric measurements were performed on the obtained AlN thin films. We have demonstrated that duration of the laser pulse is an important parameter for the quality and performances of AlN structures obtained by pulsed laser deposition.

Long period fiber gratings with suitable thin film overlayers can constitute a strong platform for the development of versatile and multi-functional sensing devices for serving diverse Biological and Health monitoring applications. Herein, we present three cases of thin film overlaid long period gratings that can find direct application in health related applications: the first example refers to a humidity sensing device utilizing PEO/CoCl 2 overlayers, and, the second refers to a simple radiation dose sensor utilizing spiropyran doped PMMA overlayers. In the final case, a vapor detection probe is demonstrated utilizing a zinc oxide (ZnO) nanorods coating. The proof of principle of these devices is presented, in conjunction with experimental results on their performance, while their application in health related applications is projected and discussed.

Zinc oxide (ZnO) is one of the most favorable and efficient oxide materials[1] in the detection of organic vapors and has been successfully used in the detection of ethanol[2] and gasoline. Furthermore, optical fiber Long Period Gratings (LPG) with a chemo- or hygro-sensitive layer deposited as outcladding coating can provide all-optical sensing capabilities[3]. Here we present a novel organic vapor sensor based on a LPG overlaid with a zinc oxide (ZnO) nanostructured film. The sensing probe has been designed for operating at room temperature while being interrogated at the 1.5 µm band. The ZnO chemosensitive layer, developed onto the cladding area of the LPG, consists of random nanorods with a characteristic diameter of 100 nm (Fig.1(a)), that were grown in an aqueous solution of Zn(NO 3 ) 2 and ammonia at 80°C, following pulsed laser deposition of a thin metallic Zn layer on the fibers[4]. For optimizing the nanostructured ZnO layer thickness with respect to the optical design and thus the sensitivity of the device, we monitored in real-time (Fig.1b) the spectrum of the LPGs during the ZnO chemical growth process; targeting specific spectral characteristics of the composite grating structure.

International audience; Using automated laser pulse temporal shaping we report on enhancing spectral emission characteristics of ablation plasmas produced by laser irradiation of brass on ultrafast time scales. For different input irradiance levels, control of both atomic and ionic species becomes possible concerning the yield and the excitation state. The improved energy coupling determined by tailored pulses induces material ejection with lower mechanical load that translates into hot gas-phase regions with higher excitation degrees and reduced particulates.

Femtosecond lasers have been used for laser induced forward transfer (LIFT) of TiO2, a wide-band semiconductor with many industrial and research applications. TiO2 polycrystalline thin films on quartz (obtained by pulsed laser deposition) were used as donors and both quartz and fluorine-doped tin dioxide coated glass substrates as acceptors. LIFT was performed at the laser wavelengths of 248 and 800 nm with pulses of 450 and 300 fs respectively. The transferred material was characterized by energy-dispersive X-ray spectroscopy, X-ray diffraction and micro-Raman spectroscopy to determine the composition and crystalline quality, and by scanning electron microscopy and atomic force microscopy to assess the surface morphology. The relation between these properties and the laser transfer conditions, including wavelength, pulse energy and acceptor substrate, are presented. © 2010 Elsevier B.V.

Optically activated indium oxide diffractive optical microstructures are demonstrated through a two step laser based fabrication method. Nonstoichiometric indium oxide thin film material grown by reactive pulsed laser deposition has been selectively transferred onto glass substrates by ultrashort pulse laser microprinting to form surface relief microstructures. Subsequent ultraviolet illumination has induced dynamic refractive index changes, which result in all optical control of the grating diffraction efficiency. The direct materials transfer process enables reproduction of the structural and physical properties of the oxide.

AlN thin films with thickness in the nanometer range were prepared by Pulsed Laser Deposition technique. The extension of PLD/RPLD for obtaining good AlN nanostructures is a consequence of high reproducibility, control of the film growth rate and stoichiometry, and low impurity contamination. We investigated in this paper the effect of laser wavelength, pulse duration, and ambient gas pressure on the composition and morphology of the deposited films. We demonstrate that we deposited stoichiometric and even textured AlN thin films by PLD from AlN targets using 3 laser sources generating pulses of 34 ns@248 nm (source A), 450 fs@248 nm (source B), and 50 fs@800 nm (source C). Plamsa investigations by Optical Emission Spectroscopy and Time-of-Flight Mass Spectrometry are in agreement with the studies of films, showing plasma richer in Al ions for source A, and the prevalent presence of AlN positive ions in the plasma generated under the action of sources B and C.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Er- doped YAG and YAP layers were grown by nanosecond (20 ns) and subpicosecond (450 fs) KrF laser ablation under a wide set of deposition conditions. Results of characterization of films crystallinity and luminescence are presented and discussed. Films grown in ns regime were almost amorphous for substrate temperature to Ts ~ 1000 oC, while films grown in subps regime were partly crystalline, even at low Ts. Film crystallinity was also studied after annealing of amorphous layers under vacuum with CO2 and KrF excimer lasers. Luminescence corresponding to Er+3 ions was observed for all samples.

3 pages, 3 figures., Thin Nd-doped potassium gadolinium tungstate [KGW or KGd(WO4)2] films are grown by pulsed laser deposition by ablation of a stoichiometric monocrystal target. Rutherford backscattering, x-ray diffraction, atomic force microscopy, and waveguide propagation analyses are performed. The as-grown films are optically active, as evidenced by the photoluminescence spectra centered at 1.068 µm. In some of the films, fine photoluminescence spectra between Stark levels are observed., This research was partially supported by the European Union, Project Nos. IC15-CT98-0807 and F-719 with the Ministry of Education and Science, Bulgaria. P.A.A. wishes to acknowledge the Scientific Committee of NATO, Spain, for financial support.

Temporally shaped, femtosecond laser pulses have been used for controlling the size and the morphology of micron-sized metallic structures obtained by using the Laser Induced Forward Transfer (LIFT) technique. We report the effect of pulse shaping on the size and morphology of the deposited structures of Au, Zn, Cr on a function of the pulse separation time ??t (from 0 to 10 ps) of double pulses of variable intensities generated by using a liquid crystal spatial light modulator (SLM). The observed differences in size and morphology are correlated with the outcome of pump-probe experiments for the study of electron-phonon scattering dynamics and subsequent energy transfer processes to the bulk in the different metals employed. We propose that in metals with weak electron-lattice coupling, the electron ballistic motion and the resulting fast electron scattering at the film surface, as well as the internal electron thermalization process are crucial to the morphology and size of the transferred material. Therefore, temporal shaping within the corresponding time scales of these processes may be used for tailoring the features of the metallic structures obtained by LIFT.

The effect of nitrogen addition and laser fluence on the atomic structure of amorphous carbon films (a-C) synthesized by femtosecond pulsed laser deposition has been studied. The chemical bonding in the films was investigated by means of X-ray photoelectron (XPS) and Raman spectroscopies. XPS studies revealed a decrease in the sp3 bonded carbon sites and an associated increase in the N-sp2C bonding sites with increasing nitrogen content in the CNx films. An increase in laser fluence from 0.36 to 1.7 J/cm2 led to a rise in sp3C sites. These results were further confirmed by Raman spectroscopy. The ID/IG ratio increased monotonically and G line-width decreased with the increase of nitrogen content in the films indicating a rise in either the number or the size of the sp2 clusters. Furthermore a visible excitation wavelength dependence study established the resonant Raman process in a-C and CNx films.

A new ethanol vapor detection probe based on an optical fiber long period grating overlaid with a zinc oxide (ZnO) nanorods layer is presented. The ZnO nanorod layer was developed onto the cladding of the fiber using aqueous chemical growth, seeded by a thin layer of metallic Zn. The growth of the ZnO nanorods overlayer onto the long period grating cladding is monitored in real time for investigating its effect on the spectral properties of the device and its subsequent role in the sensing mechanism. Results are presented, on the correlation between the growth time of the ZnO layer and the ethanol vapor detection performance. Reversible spectral changes of the notch extinction ratio of more than 4 dB were recorded for ~50 Torr of ethanol vapor concentration. In addition, photoluminescence emission studies of the ZnO overlayer performed simultaneously with the optical fiber spectral measurements, revealed significant ethanol induced changes in the intensity of the bandgap peak.