Pulsed laser deposition of KNbO₃ thin films

The laser ablation of stationary KNbO3 single crystal targets induces a Nb enrichment of the target surface. In rotated targets this effect is observed only in those areas irradiated with low laser fluence. The composition of the plasma formed close to the target surface is congruent with the target composition; however, at further distances K-deficient films are formed due to the preferential backscattering of K in the plasma. This loss may be compensated for by using K-rich ceramic targets. Best results so far have been obtained with [K]/[Nb] = 2.85 target composition, and crystalline KNbO3 films are formed when heating the substrates to 650 °C. Films formed on (100)MgO single crystals are usually single phase and oriented with the (110) film plane parallel to the (100) substrate surface. (100)NbO may coexist with KNbO3 on (100)MgO. At substrate temperatures higher than 650 °C, niobium diffuses into MgO forming Mg4Nb2O9 and NbO, leading to K evaporation from the film. Films formed on (001) alpha-Al2O3 (sapphire) show the coexistence of (111), (110), and (001) orientations of KNbO3, and the presence of NbO2 is also observed. KNbO3 films deposited on (001)LiNbO3 crystallize with the (111) plane of the film parallel to the substrate surface. For the latter two substrates the Nb diffusion into the substrate is lower than in MgO and consequently the K concentration retained in the film is comparatively larger

Optical emission properties of Nd3+ in NaBi(WO4)(2) single crystal

Room temperature optical absorption measurements of Nd3+ in NaBi(WO4)2 single crystals grown by the Czochralski method have been used to calculate the following Judd-Ofelt intensity parameters: Omega2 =30.9 × 10-20 cm2, Omega4 = 12.0 × 10-20 cm2 and Omega6 =9.3 × 10-20 cm2. Using these parameters the emission properties of Nd3+ in this host have been estimated with particular attention to the 4F3/2 energy level responsible for stimulated emission channels. The experimental branching ratios of this level are obtained from photoluminescence and agree with those calculated using the above Omegak parameters. The 4F3/2 emission has negligible non-radiative intrinsic losses and the 10 K lifetime at low Nd concentration, 0.9× 1018 cm-3, is tauexp= 143 mus. Even at 300 K and for a much higher Nd concentration, 4.0× 1019 cm-3, non-radiative losses are moderate, giving a quantum efficiency eta ap 0.85. The 4F3/2 emissions show a strongly polarized character. The largest emission cross-section occurs at lambda =1060.9 nm for the 4F3/2 rarr4I11/2 laser channel with a pi-polarized character, sigmaEMI= 16× 10-20 cm2.This work is supported by the Ministerio de Ciencia y Tecnologıa(MCy T) in Spain, under project the MAT2002-0463-C05-05. V. Volkov acknowledges support by a NATO grant. A. Mendez-Blas is supported by CONACYT (Mexico), grant No. 128118.Peer reviewe

Emission cross sections and spectroscopy of Ho3+ laser channels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho3+ laser channels in KGd(WO4)2 crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho3+ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω2=15.35×10-20 cm2, Ω 4=3.79×10-20 cm2, Ω6 =1.69×10-20 cm2. The 7-300-K lifetimes obtained in diluted (8·1018 cm-3) KGW:0.1% Ho samples are: τ(5F3)=0.9 μs, τ( 5S2)=19-3.6 μs, and τ(5F5 )=1.1 μs. For Ho concentrations below 1.5×1020 cm-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τph -1(0)=βexp(-αΔE), where β=1.4×10-7 s-1, and α=1.4×103 cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho3+ emission cross section σEM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σEM values achieved for transitions to the 5I8 level are ≈2×10-20 cm2 in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the 5I7→5I8 channel.This work was supported by Comisión Interministerial de Ciencia y Tecnología under Projects MAT99-1077 and 2FD97-0912.Peer reviewe

Tunable continuous wave and femtosecond mode-locked Yb3+ laser operation in NaLu(WO4)2

7 pages, 13 figures, 3 tables.-- PACS: 42.55.Rz; 42.60.By; 42.60.FcContinuous wave and femtosecond mode-locked laser operation of Yb3+ in the tetragonal NaLu(WO4)2 crystal host is demonstrated by pumping with a Ti:sapphire laser. Pumping with 1.8 W at 974 nm, a maximum output power of 650 mW was achieved at 1029.6 nm. The slope efficiency was in excess of 60%. The laser performance was similar for the two polarizations. By inserting a birefringent filter the output wavelength was tunable from 1010 to 1055 nm. Pulses as short as 90 fs with an average power of 50 mW were generated by passive mode locking at a repetition rate of 95 MHz. These attractive laser properties of NaLu1−xYbx(WO4)2 are related to the inhomogeneous broadening of the Yb3+ spectral features resulting from the local disorder of the host crystal. We report the spectroscopic properties of Yb3+ in the 5–300 K temperature range and the optical properties of the host at room temperature.This work was supported by Projects Nos. NMP3-CT- 2003-505580 (EU), MAT2004-21113E, and MAT2005-6354- C03-01 (Spain). A.G. (FPU2003-018), X.H. (JC12006-4015-2459) and X.M. (EX2004-1294) are supported by grants from the Spanish government. X.M. additionally acknowledges support from the European Science Foundation.Peer reviewe

Tunable continuous wave and femtosecond mode-locked Yb3+ laser operation in NaLu(WO4)2

7 pages, 13 figures, 3 tables.-- PACS: 42.55.Rz; 42.60.By; 42.60.FcContinuous wave and femtosecond mode-locked laser operation of Yb3+ in the tetragonal NaLu(WO4)2 crystal host is demonstrated by pumping with a Ti:sapphire laser. Pumping with 1.8 W at 974 nm, a maximum output power of 650 mW was achieved at 1029.6 nm. The slope efficiency was in excess of 60%. The laser performance was similar for the two polarizations. By inserting a birefringent filter the output wavelength was tunable from 1010 to 1055 nm. Pulses as short as 90 fs with an average power of 50 mW were generated by passive mode locking at a repetition rate of 95 MHz. These attractive laser properties of NaLu1−xYbx(WO4)2 are related to the inhomogeneous broadening of the Yb3+ spectral features resulting from the local disorder of the host crystal. We report the spectroscopic properties of Yb3+ in the 5–300 K temperature range and the optical properties of the host at room temperature.This work was supported by Projects Nos. NMP3-CT- 2003-505580 (EU), MAT2004-21113E, and MAT2005-6354- C03-01 (Spain). A.G. (FPU2003-018), X.H. (JC12006-4015-2459) and X.M. (EX2004-1294) are supported by grants from the Spanish government. X.M. additionally acknowledges support from the European Science Foundation.Peer reviewe

Design and analysis of CRV components in the Fermilab Mu2e experiment

The Mu2e experiment at Fermi National Accelerator Laboratory seeks to observe the ultra-rare process of a lepton changing flavor from higher to lower fermion generations. This is known theoretically as a Charged Lepton Flavor Violation (CLFV), and finding evidence of such a process would provide insight into new areas of physics outside the Standard Model. Mu2e intends on achieving higher sensitivity than any other such experiment by employing state-of-the-art detectors and trackers to collect data, and minimize all background sources of error with unprecedented precision. One of these backgrounds comes from natural cosmic-ray muons, which can produce particles that appear to be created within the detector, or can themselves be misidentified as electrons. To eliminate this source of error, a detector capable of detecting penetrating cosmic muons will be utilized. This detector, named Cosmic Ray Veto (CRV), is designed as a set of sections of additional shielding to be mounted onto the concrete shielding. Each section is made up of several modules composed of four layers of long extrusions of scintillating polystyrene and aluminum panels bonded adhesively. To achieve the desired efficiency of 0.9999, the modules of each section are stepped at their ends and interlocked with millimeter precision. In the top section of the CRV, there is a need for the ability to move modules to access electronics and other components otherwise enclosed beneath them. To facilitate access to these components, a system of lifting mechanisms, which would support and raise modules using a centered platform, is being designed. Given that this loading scenario was unaccounted for when modules were being designed, their structural integrity, as well as the performance of the adhesive used to bond them, needs to be evaluated. Critical design constraints for these mechanisms, such as platform width, rise speed, load capacity, and material selection, will be determined by evaluating modules\u27 stresses and deformations under this new loading scenario using FEA. Furthermore, shear and peel samples, made of aluminum and polystyrene bonded with the resin epoxy used to construct modules, will be built per ASTM codes D1002 and D3164 respectively. These samples will be subjected to thermal fluctuations and compression and loaded until failure. Gathered data for failure loads and modes will be evaluated to assess adhesive performance and quantify the effects of such pre-test conditions

Eduardo Arroyo contra la historia

El objetivo de este ensayo crítico es realizar un retrato biográfico del pintor y escritor Eduardo Arroyo (Madrid, 1937) para, a partir de él, llevar a cabo a un análisis temático y formal de su producción pictórica. Su obra, una de las propuestas figurativas más singulares del arte europeo contemporáneo, es testimonio de la actualidad, de lo público, al tiempo que un registro de su historia personal. Por medio de sus cuadros, Arroyo pone de manifiesto la posición crítica que ha adoptado con respecto a su contexto histórico-social, marcado durante más de tres décadas por la dictadura franquista, más tarde, por la transición democrática y en tiempos recientes por las transformaciones ocurridas en el proceso de homogeneización del mundo occidental. Así, desde comienzos de los años sesenta del siglo pasado, no ha dejado de cuestionar la validez de la historia, como disciplina que narra sucesos, de polemizar sobre los fundamentos del arte de vanguardia, además de destacar la responsabilidad ética del pintor actual en una época en la que se ve peligrar la supervivencia de su oficio. Para definir las obsesiones que han conformado su creación, detestaciones, pasiones y ambiciones, se ha extraído el ideario artístico del pintor de las fuentes primarias existentes, como son ensayos de carácter autobiográfico, artículos periodísticos, entrevistas, memorias y disertaciones públicas. En el caso de un creador locuaz, que ha sido calificado de «prestidigitador de la palabra», en virtud de las declaraciones hechas sobre los más diversos temas de la cultura, este abundante material tiene un valor extraordinario. Dichas confesiones se han puesto en relación con los ciclos pictóricos desarrollados por el artista para ser analizados a la luz de la bibliografía crítica existente sobre la materia. Entre los escritores y especialistas que han abordado su obra destacan: Francisco Calvo Serraller, Bernard Dahan-Constant, Fabienne di Rocco, Juan Goytisolo, Fernando Savater, Michel Sager, Leonardo Sciasca, Jorge Semprún, Wener Spies, José Miguel Ullán o María Zambrano..

Laser floating zone growth of Yb, or Nd, doped (Lu0.3Gd0.7)2SiO5 oxyorthosilicate single-crystal rods with efficient laser performance

Disordered crystals are being presently developed to enlarge the fluorescence bandwidth of trivalent lanthanides incorporated for generation of ultrashort (femtosecond) laser pulses in mode-locked oscillators and amplifiers, but crystal disorder induces a reduction of thermal conductivity which hampers the uniform crystal cooling after growth, leading to internal stresses. This is particularly remarkable when using the Laser Floating Zone (LFZ) growth technique; thus so far laser operation has been obtained only for LFZ-grown crystals with high thermal conductivity (κ ≥ 10 W m−1 °C−1) but without disorder, i.e. YAG, Y2O3 or REVO4. To overcome this limitation we present the LFZ growth of (Lu0.351Gd0.630Yb0.019)2SiO5 and (Lu0.307Gd0.612Nd0.081)2SiO5 refractory (melting point ≈ 1950 °C) oxyorthosilicate single-crystal rods with dimensions suitable for high power diode laser pumping, despite these crystals having medium/low thermal conductivity, κ < 4 W m−1 °C−1. Rods with ≈10 mm length and ≈1.75 mm diameter were grown in air under a CO2 laser at 10 mm h−1. X-ray diffraction analyses confirm the monoclinic C2/c structure of the obtained crystals. For the chosen ≈0.3Lu/0.7Gd ratio some of the crystals are transparent and free of macro-defects. The continuous wave laser performance of Yb3+ and Nd3+ incorporated ions is demonstrated under Ti-sapphire laser pumping in an astigmatism compensated Z-shaped optical cavity. The laser performance of these LFZ oxyorthosilicates is found to be comparable to that reported in Czochralski (Cz) grown crystals. The faster pulling rate (almost one order of magnitude larger for LFZ than for Cz), the high crystal composition purity, and the absence of crucible or atmosphere control make the LFZ technique a low cost alternative for the present needs of diode laser pumped mode-locked medium/high power laser oscillators.This work is funded by FEDER funds (COMPETE 2020 Programme), by national funds through FCT – Portuguese Foundation for Science and Technology (UID/CTM/50025/2019) as well as by Ministerio de Ciencia Innovación y Universidades (RTI2018-094859-B-I00, also FEDER co-fund) of Spain. F. Rey-García acknowledges European Union (H2020-FET-OPEN/0426), Xunta de Galicia (ED431E 2018/08) and FCT (SFRH/BPD/108581/2015) projects.Peer reviewe