E. Sarantopoulou

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.

Temperature and pressure dependence of Raman-active phonons of CaMoO4: an anharmonicity study

The Raman spectra of tetragonal CaMoO4 (scheelite structure, C4h6 space group) have been measured in the temperature range 12–1300 K. At high temperatures, the frequency and linewidth of all Raman-active phonons vary almost linearly with temperature, indicating that the three-phonon decay processes are dominant over the four-phonon ones. All Raman phonons display normal negative (∂ω/∂T) slopes throughout the temperature range, except for the lowest-frequency Bg phonon at 111.5 cm−1 which is almost temperature independent in the region 12–400 K, but then for T > 400 K it shows a slight (normal) softening with temperature. The reduced (∂ω/∂T)/ω slopes of the internal modes (vibrations of atoms within the tetrahedral MoO42− units) are an order of magnitude smaller than the respective slopes of the external ones (pure lattice modes). There are no discontinuities or sharp changes of slope in the ω(T) plots, implying that CaMoO4 remains stable over the entire temperature range. Combining the temperature-dependent Raman data of this work and the previously reported pressure-dependent Raman data on this crystal (Christofilos D, Kourouklis G A and Ves S 1995 J. Phys. Chem. Solids 56 1125), as well as the thermal expansion coefficient β(T) and compressibility κ(T) data, it has been possible to separate and evaluate quantitatively the volume (expansion) Δωvol and the pure temperature (anharmonic) Δωanh contributions to the total Δωtot shift of phonons with temperature. It has been found that for most phonons at high temperatures, the volume effect is greater than the pure temperature one, thus indicating that most of the bonds in CaMoO4 are predominantly ionic in character.

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.

LiCaAlF6:Nd3+ crystal as optical material for 157 nm photolithography

Abstract The laser induced fluorescence spectrum (LIF) of the LiCaAlF 6 :Nd 3+ single crystal, pumped by the molecular fluorine pulsed discharge laser at 157.6 nm, was obtained in the vacuum ultraviolet (VUV) region of the spectrum. The transitions originate from the edge of the 4f 2 5d electronic configuration and they were assigned to the 4f 2 5d→4f 3 interconfigurational dipole allowed transitions. The absorption spectrum of the crystal in the VUV was obtained as well. We observed twenty main dipole allowed transitions between the ground level 4 I 9/2 of the 4f 3 electronic configuration and the Stark components of the levels of the 4f 2 5d electronic configuration in the spectral range between 120 and 200 nm. The experimental results suggest that the LiCaAlF 6 :Nd 3+ crystal can be used as wavelength selective optical filter and refractive element for 157 nm photolithography.

An interpretation of the Boson peak in rare-earth ion doped glasses

Abstract The Boson peak in the Raman spectra of glasses is an ubiquitous feature. We show that doping a series of fluoride, tellurite and sulfide glass compositions with rare-earth ions, such as Pr3+, Dy3+, Nd3+, Ce3+, at concentrations between 1000 and 10,000 ppm, increases the amplitude of the Boson peak as compared to the respective undoped glasses. Further addition of rare-earth ions results in saturation and even reduction of the Boson peak ascribed to clustering of dopants and/or devitrification of glass host. Prolonged irradiation of photorefractive sulfide glasses with near-bandgap laser light also results in an increase of the Boson peak. A model is suggested for changes in the intensity and position of the Boson peak with glass composition, doping level, and after prolonged irradiation of photorefractive glasses. We propose that the presence of non-bridging anion atoms, such as F, O or S, (or anion atoms having strained bonds with increased polarizability), determines the Boson peak, as well as the solubility of rare-earth ions in glasses.

VUV and UV fluorescence and absorption studies of Pr(3+)-doped LiLuF(4) single crystals.

The laser-induced fluorescence spectrum of LiLuF(4):Pr(3+) single crystals, pumped by an F(2) pulsed-discharge molecular laser at 157 nm, was obtained in the VUV and UV regions of the spectrum at room temperature. A number of new fluorescence peaks were observed for the first time to our knowledge. They were assigned to the dipole-allowed transitions 4f5d ? 4f(2) of Pr(3+) ion. In addition, the absorption spectrum of the crystal samples was recorded. The positions of the bands with the 4f5d configuration were found to be 46 412, 53 267, and 63 397 cm(-1) from the ground state, (3)H(4), of the Pr(3+) ion. The edge (onset) of the 4f5d bands was at 45 100 cm(-1).

On the 4f25d→4f3 interconfigurational transitions of Nd3+ ions in K2YF5 and LiYF4 crystal hosts

Abstract The Laser Induced Fluorescence (LIF) spectrum of K 2 YF 5 :Nd 3+ (PFYK:Nd) and LiYF 4 :Nd 3+ (YLF:Nd) single crystals, pumped by the fluorine F 2 pulsed discharge molecular laser at 157.6 nm, was obtained in the Vacuum Ultraviolet (VUV) region of the spectrum. The fluorescence peaks were assigned to the 4f 2 5d→4f 3 dipole allowed transitions of the Nd 3+ ion. The 180 nm band of the LIF spectrum from the crystals indicates that the 4f 2 5d→4f 3 dipole transitions originate from the low Stark components of the 4 K 11/2 level of the 4f 2 5d configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well and spectroscopic assignment of the levels of the 4f 2 5d configuration was made. The electric crystal field splits all the levels of single and mixed configuration. The energy of the Stark components of the 4f 2 5d configuration in YLF:Nd was shifted by few hundred cm −1 relative to that of PFYK:Nd. We observed eleven and nine dipole transitions, between the 4 I 9/2 ground level of the 4f 3 configuration and the Stark components of the levels of the 4f 2 5d configuration of the Nd 3+ ion, in YLF and PFYK crystal hosts, respectively.

Vacuum-ultraviolet interconfigurational 4f 3 → 4f 2 5d absorption and emission studies of the Nd 3+ ion in KYF, YF, and YLF crystal hosts

The laser-induced vacuum-ultraviolet fluorescence spectra of KY3F10:Nd3+ (KYF:Nd) and YF3:Nd3+ (YF:Nd) single crystals pumped by a pulsed-discharge molecular F2 laser at 157 nm were obtained. A number of new fluorescence peaks were observed and were assigned to the 4f25d → 4f3 dipole-allowed transitions of the Nd3+ ion. The absorption spectra of LiYF4:Nd3+ (YLF:Nd), KYF:Nd, and YF:Nd crystal samples in the vacuum-ultraviolet spectral regions were also obtained. Finally, the splitting of the states of the 4f25d configuration of the Nd3+ ion, which is due to the crystal field, was observed in all the crystal samples.

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