A new series of iridium(III) mixed ligand complexes TBA[Ir(ppy)(2)(CN)(2)] (1), TBA[Ir(ppy)(2)(NCS)(2)] (2), TBA[Ir(ppy)(2)(NCO)(2)] (3), and [Ir(ppy)(2)(acac)] (4) (ppy = 2-phenylpyridine; acac = acetoylacetonate, TBA = tetrabutylammonium cation) have been developed and fully characterized by UV-vis, emission, IR, NMR, and cyclic voltammetric studies. The lowest energy MLCT transitions are tuned from 463 to 494 nm by tuning the energy of the HOMO levels. These complexes show emission maxima in the blue, green, and yellow region of the visible spectrum and exhibit unprecedented phosphorescence quantum yields, 97 +/- 3% with an excited-state lifetimes of 1-3 micros in dichloromethane solution at 298 K. The near-unity quantum yields of these complexes are related to an increased energy gap between the triplet emitting state and the deactivating e(g) level that have been achieved by meticulous selection of ligands having strong ligand field strength. Organic light-emitting devices were fabricated using the complex 4 doped into a purified 4,4'-bis(carbazol-9-yl)biphenyl host exhibiting a maximum of the external quantum efficiencies of 13.2% and a power efficiency of 37 lm/W for the 9 mol % doped system.

We present a novel plasmonic antenna geometry - the double resonant antenna (DRA) - that is optimized for second-harmonic generation (SHG). This antenna is based on two gaps coupled to each other so that a resonance at the fundamental and at the doubled frequency is obtained. Furthermore, the proximity of the localized hot spots allows for a coupling and spatial overlap between the two field enhancements at both frequencies. Using such a structure, both the generation of the second-harmonic and its re-emission into the far-field are significantly increased when compared with a standard plasmonic dipole antenna. Such DRA are fabricated in aluminium using electron beam lithography and their linear and nonlinear responses are studied experimentally and theoretically.

High-quality crystals of monoclinic KLu(WO4)2, shortly KLuW, were grown with sizes sufficient for its characterization and substantial progress was achieved in the field of spectroscopy and laser operation with Yb 3+ -and Tm 3+ -doping. We review the growth methodology for bulk KLuW and epitaxial layers, its structural, thermo-mechanical, and optical properties, the Yb 3+ and Tm 3+ spectroscopy, and present laser results obtained in several operational regimes both with Ti:sapphire and direct diode laser pumping using InGaAs and AlGaAs diodes near 980 and 800 nm, respectively. The slope efficiencies with respect to the absorbed pump power achieved with continuous-wave (CW) bulk and epitaxial Yb:KLuW lasers under Ti:sapphire laser pumping were ≈ 57 and ≈ 66%, respectively. Output powers as high as 3.28 W were obtained with diode pumping in a simple two-mirror cavity where the slope efficiency with respect to the incident pump power reached ≈ 78%. Passively Q-switched laser operation of bulk Yb:KLuW was realized with a Cr:YAG saturable absorber resulting in oscillation at ≈ 1031 nm with a repetition rate of 28 kHz and simultaneous Raman conversion to ≈ 1138 nm with maximum energies of 32.4 and 14.4 µJ, respectively. The corresponding pulse durations were 1.41 and 0.71 ns. Passive mode-locking by a semiconductor saturable absorber mirror (SESAM) produced bandwidth-limited pulses with duration of 81 fs (1046 nm, 95 MHz) and 114 fs (1030 nm, 101 MHz) for bulk and epitaxial Projection of the KLu(WO4)2 structure parallel to the b crystallographic direction [010].Yb:KLuW lasers, respectively. Slope efficiency as high as 69% with respect to the absorbed power and an output power of 4 W at 1950 nm were achieved with a diodepumped Tm:KLuW laser. The slope efficiency reached with an epitaxial Tm:KLuW laser under Ti:sapphire laser pumping was 64 %. The tunability achieved with bulk and epitaxial Tm:KLuW lasers extended from 1800 to 1987 nm and from 1894 to 2039 nm, respectively.

Mode locking of an Yb-doped bulk laser in the 1 microm spectral range using a single-walled carbon nanotube saturable absorber (SWCNT-SA) is demonstrated for the first time, to our knowledge. Passive mode locking of an Yb:KLuW laser resulted in nearly transform-limited pulses as short as 115 fs at 1048 nm. In addition, the nonlinear response of the SWCNT-SA was measured, yielding a modulation depth of 0.25% and a relaxation time of 750 fs.

High-quality monoclinic KY͑WO 4 ͒ 2 optical waveguides were grown by liquid-phase epitaxy, and laser operation of an Yb-doped KY͑WO 4 ͒ 2 waveguide was demonstrated for the first time to our knowledge. Continuous-wave laser emission near 1 m was achieved with both surface and buried planar waveguides. An output power of 290 mW was obtained in the fundamental mode and the slope efficiency was above 80%. OCIS codes: 140.3070, 140.3380, 140.5680, 230.7390, 310.1860OCIS codes: 140.3070, 140.3380, 140.5680, 230.7390, 310. , 310.2790 Crystals of monoclinic KY͑WO 4 ͒ 2 (KYW) doped with different rare-earth ions are recognized as very promising materials for solid-state lasers operating at room temperature, both in pulsed and continuouswave (cw) mode. 1,2 Due to its high refractive indices, of the order of 2.0, KYW is highly suitable for the fabrication of integrated optical devices. Rare-earth ions incorporated into KYW exhibit very high absorption and emission cross sections. In particular, the Yb 3+ ion in KYW has an absorption maximum near 981 nm with a cross section, for polarization parallel to the N m principal optical axis, ϳ15 times larger than that of YAG:Yb. The short absorption length in highly doped KYW:Yb together with an extremely small laser quantum defect as low as 1.6% (Ref. 3) makes this material a favorable candidate for the thin-disk laser concept, 4 where the active medium is a thin crystal or deposited layer. Recently, cw laser operation normal to a thin layer of KYW doped with 20 at. % Yb (with respect to the Y site) on a KYW substrate was demonstrated and the maximum output power reached 40 mW at 1030 nm. © 2006 Optical Society of America 5In this Letter we report the epitaxial growth of high-quality optical waveguides and, for the first time to our knowledge, on waveguide laser operation based on a double tungstate crystal composite. The waveguide geometry provides potentially high pumppower densities and excellent overlap of pump and resonator modes. This approach requires fabrication of large-area, defect-free thin layers of KYW:Yb on appropriate substrates, having small lattice mismatch and close-to-perfect interfaces between the layer and the substrate to ensure low-loss propagation.Liquid-phase epitaxy (LPE) is a well-known technique for producing high-quality oxide films for laser applications, in which a single-crystal layer can be grown from a molten solution on an oriented singlecrystal substrate.6 During LPE of rare-earth-iondoped KYW layers employing a low-temperature chloride solvent, 7 3D island nucleation generated insertion defects, which limited the maximum layer thickness to approximately 10 m and led to nonoptimum interface quality.The tungstate solvent K 2 W 2 O 7 , which we employed successfully in the present work, can potentially offer larger thickness and good layer quality.5,8 Undoped 1 mm thick KYW crystals grown by a modified Czochralski method with laser-grade polished (010) faces served as substrates. Building on previous work, 5 we employed the vertical dipping tech...

It has been recognized that the monoclinic double tungstates KY(WO 4) 2 , KGd(WO 4) 2 , and KLu(WO 4) 2 possess a high potential as rare-earth-ion-doped solid-state laser materials, partly due to the high absorption and emission cross sections of rare-earth ions when doped into these materials. Besides, their high refractive indexes make these materials potentially suitable for applications that require optical gain and high power in integrated optics, with rather high integration density. We review the recent advances in the field of bulk lasers in these materials and present our work toward the demonstration of waveguide lasers and their integration with other optical structures on a chip.

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