Concepción Cascales

Spectroscopy and Lasing of Yb-Doped

Tetragonal (space group f4 macr) single crystals of NaY(WO4)2 doped with Yb to a density of 4.52 times 1020 cm-3 have been employed as laser active materials for the 1-mum spectral range, operating at room temperature. Using Ti:sapphire laser pumping, slope efficiencies as high as 74.6% were achieved without special cooling for the pi-polarization. The Yb-laser was continuously tunable from 1003.7 to 1073.0 nm with a birefringent filter. Pulses as short as 53 fs were obtained at 1035 nm by SESAM passive mode-locking with intracavity dispersion compensation and additional extracavity pulse compression using analogous prism pairs. Experimental data on the spectroscopic properties of Yb3+ in the 5-300 K temperature range and the room temperature optical properties of this novel Yb-host is also presented.

{\hbox {NaY}}{({\hbox {WO}}_{4})}_{2}

Lasing of Yb3+ in a disordered single crystal host, NaGd(WO4)2, is reported. Pump efficiencies as high as 20% and slope efficiencies as high as 30% are achieved for both sigma- and pi-polarizations with Ti:sapphire laser pumping. The emission of Yb:NaGd(WO4)2 is centered near 1030 nm. Tunability between 1016 and 1049 nm is obtained with a Lyot filter.

: Tunable and Femtosecond Mode-Locked Laser Operation

We report, for the first time to our knowledge, femtosecond-pulse operation of a Tm,Ho:NaY(WO(4))(2) laser at around 2060 nm. Transform-limited 191 fs pulses are produced with an average output power of 82 mW at a 144 MHz pulse repetition frequency. Maximum output power of up to 155 mW is generated with a corresponding pulse duration of 258 fs. An ion-implanted InGaAsSb quantum-well-based semiconductor saturable absorber mirror is used for passive mode-locking maintenance.

Tunable laser operation of ytterbium in disordered single crystals of Yb:NaGd(WO4)2.

Zn(C17H8F6O4) is the first example of a fluoro-lined nanotube organo-inorganic 3D polymeric chiral structure, which possesses two different types of isolated channels, one of them being laid out with a double spiral of CF3-groups from the ligand molecule; the structure is a new uninodal 4-connected net that only exists when bent ligands connect the centres, and the compound exhibits selective sorption and catalytic chiral recognition properties.

Femtosecond (191 fs) NaY(WO4)2 Tm,Ho-codoped laser at 2060 nm.

The disordered crystal LiGd0.936Yb0.064(MoO4)2 was grown with high optical quality by the flux method using Li2MoO4 as a solvent. The crystal possesses tetragonal symmetry belonging to the space group I4¯, with two nonequivalent sites occupied by the dopant. Spectroscopic studies at 5 and 300 K provided information on the Stark energy-level splitting and the absorption and emission cross sections of the Yb3+ ion. Laser operation of Yb3+ was obtained for the first time in such a Li-containing double tungstate or molybdate. The tuning range with a Ti:sapphire laser pumping extended over ∼32nm for the σ polarization and 23nm for the π polarization. Without a tuning element the laser performance was similar for the two polarizations. By using a 10% transmission output coupler, a maximum output power of ≈470 mW was obtained with a slope efficiency η=64.5% and the absorbed pump power at threshold was 520 mW. Laser operation was also achieved by pumping with a tapered diode laser and a fiber-coupled diode laser module, with a Yb laser output power of 0.66W in the latter case.

One teflon®-like channelled nanoporous polymer with a chiral and new uninodal 4-connected net: sorption and catalytic properties

The polarized optical absorption (OA) and photoluminescence of Pr3+ doped KGd(WO4)2 (KGW) single crystals have been measured at selected temperatures between 7 and 300 K. For the studied Pr concentrations, [Pr] = 0.03×1020-1.9×1020 cm-3, a unique site is observed. 74 energy levels were experimentally determined for this site and labelled with the appropriate A or B irreducible representations corresponding to the C2 symmetry of the Gd point site in KGW. The set was fitted to a Hamiltonian of adjustable parameters including free-ion as well as real Bqk and complex Sqk crystal-field parameters. A good simulation of the experimental crystal field energies was achieved with a root mean square deviation σ = 15.3 cm-1. Distortions in the oxygen bonds to Pr3+ are found to contribute to the broadening of some OA bands, particularly those related to the 1D2 multiplet. The OA edge is determined by the interconfigurational 4f→4f15d1 Pr3+ transition peaking at 34 200 cm-1. From the average 300 K OA cross sections the radiative lifetimes of the Pr3+ multiplets have been calculated considering the standard and modified Judd-Ofelt (JO) theories. A better agreement with the experimental results is obtained by the standard theory: the average JO parameters obtained at 2 = 12.0×10-20 cm2, 4 = 8.15×10-20 cm2 and 6 = 2.64×10-20 cm2. Electrons excited to the 3P0 multiplet decay very efficiently to the 1D2 multiplet even at 15 K. In samples with [Pr]≥0.3×1020 cm-3 the excitation of the 1D2 multiplet decays non-radiatively by an electric dipole-dipole transfer between Pr neighbours.

Growth, spectroscopy, and tunable laser operation of the disordered crystal LiGd(MoO 4 ) 2 doped with ytterbium

Continuous 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 1.8W at 974nm, a maximum output power of 650mW was achieved at 1029.6nm. 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 1010to1055nm. Pulses as short as 90fs with an average power of 50mW were generated by passive mode locking at a repetition rate of 95MHz. 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 5–300K temperature range and the optical properties of the host at room temperature.

Optical spectroscopy of Pr3+ in KGd(WO4)2 single crystals

Tetragonal zircon-type codoped Yb, Ln-GdVO(4) (Ln=Tm, Ho, Er) upconverting nanocrystals with square and rectangular sections were prepared through an efficient low-temperature hydrothermal synthesis. Further processing that combined annealing at 600 °C followed by coating of the surface with a uniform 5 nm-shell of SiO(2) resulted in a significant improvement of the intensity of the upconverted emitted visible light following near-infrared (~980 nm) diode laser excitation with respect to raw hydrothermal nanocrystals. Strong tunable color and bright visible light composed of red-green, blue and green emissions from Ho(3+), Tm(3+) and Er(3+), respectively, were generated by adjusting the Yb-Ln composition of these silica-coated nanocrystals. Based on calculations of CIE color coordinates, nearly ideal white upconversion light was achieved for samples of composition Gd(0.829)Yb(0.15)Tm(0.01)Ho(0.009)Er(0.002)VO(4).

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

A new zeolite-type structure is adopted by (NH(4))(+)[M(NH(3))(2)](+)(Ge(9)O(19))(2-) (M=Cu, Ag; shown in the picture). These compounds are the first microporous germanates containing a transition metal complex inside their tunnels. The large separation between the metal centers and the unhindered access of reactants to these active sites through uniformly sized channels make these materials a good point of departure for designing new catalysts.

Enhanced upconversion multicolor and white light luminescence in SiO2-coated lanthanide-doped GdVO4 hydrothermal nanocrystals

Pure and Er-doped ([Er]crystal≤2.4 × 1020 cm−3), NaBi(WO4)2 (NBW), NaBi(MoO4)2, and LiBi(MoO4)2 crystals have been grown by the Czochralski method. The three crystal hosts have similar structural and optical properties. The noncentrosymmetric space group I4¯ (No. 82) crystallographic structure has been established through 300 K single-crystal x-ray and neutron (for NBW only) diffraction. Er3+ energy levels were determined experimentally and simulated in the S4 symmetry through a crystal-field analysis. With this background, the large spectroscopic bandwidths observed were ascribed to the presence of two 2b and 2d sites for Er3+ and to different short-range Na+ and Bi3+ distributions around both sites. The radiative properties of Er3+ are described by the Judd-Ofelt theory achieving branching ratios and radiative lifetimes for transitions useful as laser channels. The 4I13/2—>4I15/2 laser channel (λ≈1.5 μm) shows a peak emission cross-section σEMI(λ≈1530 nm)≈0.5×10−20 cm2 and a quantum efficiency η∞0.68 to 0.74. The laser emission is envisaged to be tunable by Δλ≈100 nm.