A.C. Cefalas

Efficient LaF3 :Nd3+-based vacuum-ultraviolet laser at 172 nm

Vacuum-ultraviolet (VUV) laser radiation at 172 nm has been obtained from a solid-state LaF3:Nd3+-based laser pumped by a pulsed-discharge molecular F2 laser at 157 nm. The maximum slope efficiency of the solid-state laser described in this experiment was 21% (14% conversion efficiency), and the maximum output energy at 172 nm was 0.4 mJ for a nonoptimized optical cavity. This finding introduces serious prospects for realizing versions of active-medium-plus-source tunable VUV laser devices.

Nucleation and crystallization of CaCO3 in applied magnetic fields

The formation of calcium carbonate is not only a common ionic reaction that takes place in natural processes, but also creates a problem known as scaling, which is present in our every day life and in various industrial processes and technologies. In spite of the simplicity of the reaction there is considerable variability in the properties of the solid product, such as: crystal form, particle size distribution, electro-kinetics potential, etc. The influence of the magnetic field on calcium carbonate precipitation has been known for a long time but despite a lot of effort, which has been made to explain this effect, researchers still disagree on the mechanism(s) responsible for it. The focus of our research work was to follow systematically the influence of the magnetic field on the crystal form of calcium carbonate precipitated from low concentration water solutions. By changing the strength of the field and the flow rate of the water through the system the calcite/aragonite/vaterite ratio varied. The crystal form and the particle-size distribution of the precipitated calcium carbonate were determined by using X-ray analyses and TEM. The theoretical part of the work was to study the mechanism of the influence of the magnetic field on the nucleation and further crystallization of calcium carbonate. Starting from ab initio calculations the fundamental physics knowledge was used to propose a mechanism for a better understanding of the phenomena.

Amplification characteristics of a discharge excited F2 laser

Abstract The small signal gain coefficient and the saturation intensity of a molecular-fluorine pulsed-discharge laser at 157 nm have been measured using two discharge devices in the oscillator-amplifier configuration. At 3 atm total gas pressure and 1·5 cm electrode spacing the small signal gain coefficient and the saturation intensity of the 3Π2g → 3ΠI2u transition were measured to be 5·2% cm−1 and 5 MW cm−2 respectively.

On the Development of New VUV and UV Solid State Laser Sources for Photochemical Applications

Laser action in the VUV and UV region of the spectrum at 172 nm and at 260 nm had been obtained from LaF3:Nd3

Vacuum ultraviolet and ultraviolet fluorescence and absorption studies of Er3+‐doped LiLuF4 single crystals

The laser induced fluorescence spectrum of LiLuF4:Er3+ single crystals, pumped by an F2 pulsed discharge molecular laser at 157 nm, was obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum at room temperature. A number of new fluorescence peaks were observed for the first time. They were assigned to the dielectric dipole allowed transitions 4f105d→4f11 of the Er3+ ion. In addition, the absorption spectrum of the same crystal samples was recorded. The positions of the bands within the 4f105d configuration were located at 65 098, 69 198, 71 422, 74 343, and 76 916 cm−1. The edge of the 4f105d bands was at 63 046 cm−1.

VUV and UV fluorescence and absorption studies of Nd3+ and Ho3+ ions in LiYF4 single crystals

Abstract The laser induced fluorescence spectra of LiYF 4 :ND 3+ (YLF:Nd) and LiYF 4 :Ho 3+ (YLF:Ho) single crystals, pumped by an F 2 pulsed discharge molecular laser at 157 nm were obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum. With this pumping arrangement a number of new fluorescence peaks were observed for the first time. They are assigned to the dipole allowed transitions 4f 2 5d→4f 3 and 4f 9 5d→4f 10 of the Nd 3+ and Ho 3+ ions, respectively. The absorption spectra of the same crystal samples in the VUV and UV spectral regions were taken as well.

Selective aggregation of PAMAM dendrimer nanocarriers and PAMAM/ZnPc nanodrugs on human atheromatous carotid tissues: a photodynamic therapy for atherosclerosis

Photodynamic therapy (PDT) involves the action of photons on photosensitive molecules, where atomic oxygen or OH− molecular species are locally released on pathogenic human cells, which are mainly carcinogenic, thus causing cell necrosis. The efficacy of PDT depends on the local nanothermodynamic conditions near the cell/nanodrug system that control both the level of intracellular translocation of nanoparticles in the pathogenic cell and their agglomeration on the cell membrane. Dendrimers are considered one of the most effective and promising drug carriers because of their relatively low toxicity and negligible activation of complementary reactions. Polyamidoamine (PAMAM) dendrite delivery of PDT agents has been investigated in the last few years for tumour selectivity, retention, pharmacokinetics and water solubility. Nevertheless, their use as drug carriers of photosensitizing molecules in PDT for cardiovascular disease, targeting the selective necrosis of macrophage cells responsible for atheromatous plaque growth, has never been investigated. Furthermore, the level of aggregation, translocation and nanodrug delivery efficacy of PAMAM dendrimers or PAMAM/zinc phthalocyanine (ZnPc) conjugates on human atheromatous tissue and endothelial cells is still unknown.In this work, the aggregation of PAMAM zero generation dendrimers (G0) acting as drug delivery carriers, as well as conjugated G0 PAMAM dendrimers with a ZnPc photosensitizer, to symptomatic and asymptomatic human carotid tissues was investigated by using atomic force microscopy (AFM). For the evaluation of the texture characteristics of the AFM images, statistical surface morphological and fractal analytical methodologies and Minkowski functionals were used. All statistical quantities showed that the deposition of nanodrug carriers on healthy tissue has an inverse impact when comparing to the deposition on atheromatous tissue with different aggregation features between G0 and G0/ZnPc nanoparticles and with considerably larger G0/ZnPc aggregations on the atheromatous plaque. The results highlight the importance of using PAMAM dendrimer carriers as a novel and promising PDT platform for atherosclerosis therapies.

On the VUV and UV 4f7(8S)5d→4f8 interconfigurational transitions of Tb3+ ions in LiLuF4 single crystal hosts

Abstract The laser induced fluorescence spectrum of Tb 3+ ions in LiLuF 4 single crystals, pumped by a fluorine pulsed discharge molecular laser at 157.6 nm, was obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum. The 4f 7 5d→4f 8 dipole allowed transitions originate from the Stark components and the edge of the levels of the 4f 7 ( 8 S )5d electronic configuration. The LIF spectra were interpreted on the basis of phonon trapping and phonon reabsorption within the levels of the 4f 7 5d electronic configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well. We observed eight transitions between the ground level 4f 8 ( 7 F 6 ) and the Stark components of the levels of the 4f 7 ( 8 S )5d electronic configuration and five transitions between the ground level 4f 8 ( 7 F 6 ) and the Stark components of the levels of the 4f 7 ( 6 P )5d electronic configuration. The edge of the levels of the 4f 7 5d electronic configuration was found to be at 45.2×10 3 ±0.2×10 3 cm −1 and the band gap of the crystal host was 77.6×10 3 ±0.3×10 3 cm −1 wide.

Thermionic field emission in gold nitride Schottky nanodiodes

We report on the thermionic field emission and charge transport properties of gold nitride nanodomains grown by pulsed laser deposition with a molecular fluorine laser at 157 nm. The nanodomains are sandwiched between the metallic tip of a conductive atomic force microscope and a thin gold layer forming thus a metal-semiconductor-metal junction. Although the limited existing data in the literature indicate that gold nitride was synthesized previously with low efficiency, poor stability, and metallic character; in this work, it is shown that gold nitride nanodomains exhibit semiconducting behavior and the metal-semiconductor-metal contact can be modeled with the back-to-back Schottky barrier model. From the experimental I-V curves, the main charge carrier transport process is found to be thermionic field emission via electron tunneling. The rectifying, near symmetric and asymmetric current response of nanocontacts is related to the effective contact area of the gold nitride nanodomains with the metals. A l...

Surface modification of polyhedral oligomeric silsesquioxane block copolymer films by 157 nm laser light

Thin films of ethyl polyhedral oligomeric silsesquioxane (ethyl-POSS) containing polymers at different compositions were chemically modified using laser irradiation at 157 nm. The irradiation caused photodissociation of C–O and C–H bonds followed by the formation of new chemical bonds. The content of Si–O and C–O bonds increased, as did the surface hardness. Vacuum ultraviolet (VUV) absorption, mass spectrometry, x-ray photoelectron spectroscopy, and atomic force microscopy imaging and indentation were used to evaluate the effects of the 157 nm irradiation. The chemical modification was restricted to a thin surface layer. The layer depth was determined by the penetration depth of the 157 nm VUV photons inside the thin copolymer layer. With prolonged VUV irradiation, the absorbance of the polymers increased, eventually becoming saturated. The chemical changes were accompanied by surface hardening, as evidenced by the increase in the Young’s modulus from 4 to 24 GPa due to glassification of the irradiated p...