R. Solé

Growth of β-KGd1-xNdx(WO4)2 single crystals in K2W2O7 solvents

Abstract High-temperature solutions of the K2W2O7-KGd1 − xNdx(WO4)2 system have been investigated and β-KGd1 − xNdx(WO4)2 (KGW:Nd) single crystals were grown. The concentration and temperature regions of the KGW:Nd phase as well as the thermal dependence of their solubility for x = 0, 0.05, 0.10, 0.25, 0.50 and 1.00 were determined. These results were supported by X-ray and cell parameters data. EPMA analyses were used to determine the Nd3+ distribution coefficient for different initial compositions of the solution. The obtained data suggested that K2W2O7 is a suitable solvent for KGW:Nd single crystal growth. Transmission measurements have also been included as a first approach to the optical behaviour of the growth crystals.

Structure, crystal growth and physical anisotropy of KYb(WO4)2, a new laser matrix

The crystal structure of monoclinic KYb(WO4)2 (KYbW) crystals has been refined (in space group C2/c) at room temperature by using single-crystal X-ray diffraction data. KYbW undoped crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, {\bar{1}11}, {010} and {310} faces, which basically define their habit. The linear thermal expansion tensor has been determined and the principal axis with maximum thermal expansion (\alpha ^{\,\prime}_{33} = 16.68 × 10−6 K−1), {\bf X}^{\,\prime}_{3}, was located 12° from the c axis. Its principal {\bf X}^{\,\prime}_{1}, {\bf X}^{\,\prime}_{2} and {\bf X}^{\,\prime}_{3} axes are [302], [010] and [106] directions, respectively, in the crystallographic system. The optical tensor has been studied at λ = 632.8 nm at room temperature; two principal axes, Ng and Nm, are located in the ac plane, while the other, Np, is parallel to [010]. The principal axis with maximum refractive index (ng = 2.45), Ng, was located 19° from the c axis.

Efficient tunable laser operation of Tm:KGd(WO/sub 4/)/sub 2/ in the continuous-wave regime at room temperature

Tm:KGd(WO/sub 4/)/sub 2/ is studied as a three-level laser on the /sup 3/F/sub 4/ /spl rarr/ /sup 3/H/sub 6/ transition and a tunable source in the 2-/spl mu/m spectral range, operating at room temperature. An overall tunability extending from 1790 to 2042 nm is achieved with maximum output powers of 400 mW for an absorbed pump power of 1 W. Various doping levels, pump wavelengths and polarization configurations are compared and the advantages of the monoclinic double tungstates over other Tm-hosts are outlined.

Laser operation of epitaxially grown Yb:KLu(WO/sub 4/)/sub 2/--KLu(WO/sub 4/)/sub 2/ composites with monoclinic Crystalline structure

Epitaxial monoclinic double tungstate composites based on the strongly anisotropic KLu(WO/sub 4/)/sub 2/ (KLuW) were grown with high crystalline quality and laser operation of ytterbium was demonstrated for the first time. Highly efficient CW laser emission of an Yb:KLuW-KLuW crystal was achieved near 1030 nm. The 100-/spl mu/m-thick Yb:KLuW layer was pumped at wavelengths near 980 nm by a tapered diode laser as well as by a Ti:sapphire laser. More than 500 mW of CW output power and slope efficiencies up to 66% were obtained at room temperature without cooling.

Continuous-wave laser oscillation of Yb/sup 3+/ in monoclinic KLu(WO/sub 4/)/sub 2/

The strongly anisotropic monoclinic double tungstate crystal KLu(WO/sub 4/)/sub 2/ was doped with Yb/sup 3+/ ions and shown to be a highly efficient active laser medium in the 1-/spl mu/m spectral range for continuous-wave room-temperature operation, very suitable for pumping with InGaAs laser diodes.

1.48 and 1.84 μm thulium emissions in monoclinic KGd(WO4)2 single crystals

By exciting at 788 nm, we have characterized the near infrared emissions of trivalent thulium ions in monoclinic KGd(WO4)2 single crystals at 1.48 and 1.84 μm as a function of dopant concentration from 0.1% to 10% and temperature from 10 K to room temperature. We used the reciprocity method to calculate the maximum emission cross-section of 3.0×10−20 cm2 at 1.838 μm for the polarization parallel to the Nm principal optical direction. These results agrees well with the experimental data. Experimental decay times of the 3H4→3F4 and 3F4→3H6 transitions have been measured as a function of thulium concentration.

Optical characterization of Tm3+-doped KGd(WO4)2 single crystals

Abstract In this paper we present the optical characterization of KGd(WO4)2 single crystals doped with thulium ions at several concentrations from 0.1% to 10% grown by the top-seeded-solution-growth slow-cooling method. Polarized optical absorption was carried out between 350 nm (28,571 cm−1) and 2 μm (5000 cm−1), at room temperature (RT) and low temperature (6 K). We determined the splitting of the corresponding excited energy levels of thulium in KGd(WO4)2. Luminescence spectra was obtained between 300 nm (33,333 cm−1) and 2.5 μm (4000 cm−1) by pumping at 688 nm (14,535 cm−1) and 788 nm (12,690 cm−1) from 10 K to RT. Finally, we proposed a 788 nm pumping scheme for the generation of the emissions.

Erbium spectroscopy and 1.5-/spl mu/m emission in KGd(WO/sub 4/)/sub 2/: Er,Yb single crystals

We grew good-optical-quality KGd(WO/sub 4/)/sub 2/ single crystals doped with erbium and ytterbium ions at several concentrations of dopants using the top-seeded-solution growth slow-cooling method (TSSG). We performed the spectroscopic characterization of this material related to the 1.5-mm infrared emission of erbium which is interesting for laser applications. To do this, we carried out polarized optical absorption at room temperature (RT) and at low temperature (6 K) and performed luminescence studies of the emission and lifetime. We obtained the 1.5-mm emission of erbium after selective laser pump excitation of the ytterbium ion and energy transfer between the two ions. The maximum emission cross section for 1.5 mm was about 2.56/spl times/10/sup -20/ cm/sup 2/ for the polarization of light with the electric field parallel to the N/sub m/ principal optical direction. This value was higher than for other erbium-doped materials with application in solid-state lasers such as LiYF/sub 4/:Er(YLF:Er), Y/sub 3/Al/sub 5/O/sub 12/:Er(YAG:Er), YAlO/sub 3/:Er, and Al/sub 2/O/sub 3/:Er.

Green luminescence of Er3+ in stoichiometric KYb(WO4)2 single crystals

We grew good-optical-quality KYb(WO4)2 single crystals doped with erbium ions by the top seeded solution growth slow cooling method. Optical absorption of erbium was performed at room temperature (RT) and at 6 K. Green photoluminescence of erbium was achieved at RT and 6 K after selective excitation of ytterbium ions at 940 nm (10 638 cm−1). The splitting of all found excited energy levels and the ground energy level of erbium in KYb(WO4)2 is presented derived from the accurate absorption and emission measurements, respectively. The lifetime of the Stokes and the anti-Stokes green emissions of erbium were measured after excitation at 488 nm (20 490 cm−1) and 940 nm(10 638 cm−1), respectively. We propose applying the up-conversion model to the observed green emission.

Liquid phase epitaxy of KTiOPO4 on KTi1-xGexOPO4 substrates.

Liquid phase epitaxy of KTiOPO4 on KTi1-xGexOPO4 substrates. We have Studied the liquid phase epitaxy growth or KTiOPO4 on several faces of KTi1-xGexOPO4 substrates as a function of the crystal face, growth time and level of substrate Ti in the substrate. The best quality films were oil the {100} and {201} faces. Only slight growth steps were observed oil these faces in some experiments. The lowest quality of the films was on the {110} and {011} faces and the typical defects were hillocks. The worst quality of epitaxial growth was oil the {101} face and pyramidal growth was detected in all cases. There was not observed diffusion of the Ge from the substrates to the film and the maximal change in refractive indices between substrate and film was of the order of 0.01