Xiumei Han

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

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.

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

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.

Continuous-wave tunable and femtosecond mode- locked laser operation of Yb:NaY"MoO 4 … 2

Continuous-wave and mode-locked laser operations of Yb3+ in the disordered flux-grown NaY(MoO4)2 are demonstrated. The maximum slope efficiency achieved with Ti:sapphire and diode laser pumping is 63% and 38.6%, respectively. The continuous-wave tunability extends from 1005 to 1059 nm, and laser pulses with a duration of 91 fs at 1026 nm are obtained at a repetition rate of 90 MHz and an average power of 20 mW under Ti:sapphire laser pumping. Yb3+-doped NaY(MoO4)2 is locally disordered and exhibits the largest absorption and emission cross sections known so far for tetragonal double tungstates or molybdates.

Continuous-wave laser operation of Tm and Ho co-doped NaY(WO 4 ) 2 and NaLu(WO 4 ) 2 crystals

Tetragonal single crystals of NaT(WO(4))(2) (T = Y or Lu) co-doped with Tm(3+) and Ho(3+) ions have been employed for broadly tunable and efficient room-temperature laser operation at around 2 mum. With Ti:sapphire laser pumping at 795 nm, a slope efficiency and a maximum output power as high as 48% and 265 mW, respectively, have been achieved at 2050 nm from a Tm,Ho:NaY(WO(4))(2) crystal. Tuning from 1830 nm to 2080 nm has also been obtained using an intracavity Lyot filter.

Efficient mid-infrared laser operation of Li 3 Lu 3-x Tm x Ba 2 (MoO 4 ) 8 disordered crystal

Tm-doped Li(3)Lu(3)Ba(2)(MoO(4))(8) monoclinic (C2/c) crystals were grown by the TSSG-method. Details of the crystal growth and Tm(3+) spectroscopy are presented. 514 mW of laser light at 1940 nm was obtained with 71.4% of slope efficiency in quasi-cw operation mode. The laser was tuned in the 1853-2009 nm range. The crystal shows local disorder due to the shared occupancy by Li and Lu of the same 8f lattice site, this confers potential applications for mode-locked sub-200 fs laser pulses.

Spectroscopy and efficient laser operation near 1.95μm of Tm3+ in disordered NaLu(WO4)2

Continuous wave and tunable laser operation at room temperature is demonstrated with single crystals of Tm-doped NaLu(WO4)2. Under Ti:sapphire laser pumping and tuning by an intracavity Lyot filter, the Tm3+ emission extended from 1799to2026nm. The maximum output power exceeded 0.5W and the maximum slope efficiency with respect to the absorbed power was above 58%. These good laser properties are related to the locally disordered tetragonal (I4¯) structure of the crystalline host. Using low temperature spectroscopy and energy level simulation methods, the energy levels and spectroscopic properties of Tm3+ have been shown to be compatible with the S4 site symmetry. This allowed the reliable determination of the emission cross sections related to the laser transitions.

Mode-locked laser operation of Indium-modified Yb:KY(WO 4 ) 2 single crystal

We report the first pulsed laser operation of an Indium-modified Yb:KY(WO4)2 crystal. Indium incorporation enlarges the broadening of the Yb3+ optical bands, reduces crystal lattice parameters and increases n(p) refractive index. A KY0.8In0.07Yb0.13(WO4)2 crystal pumped at 981 nm with a Ti-sapphire laser in a SESAM modulated resonator produces at 300 K self-starting and stable mode-locking. The shortest laser pulses achieved were centred at λ = 1041.1 nm, have a duration of 96 fs with average power of 134 mW and repetition rate of 103.5 MHz (1.3 nJ/pulse).

White and full color upconversion film-on-glass displays driven by a single 978 nm laser

White and full-color displays based on upconversion (UC) processes in multilayered NaLu₁-x-yYbxTmy(WO₄)₂/NaLu₁-x-zYbxHoz(WO₄)₂ films deposited on 20 × 20 mm² Pyrex glass substrates are demonstrated by scanning with a 978 nm focused beam from a diode laser. Moreover, spatially resolved red, green and blue pixels are selected by focusing the excitation light at different depths on three stacked films with compositions individually optimized for UC emission of each fundamental color. The highest temperature used in synthesis/deposition process was 580 °C allowing the use of glass substrates.

Thermal Characterization, Crystal Field Analysis and In-Band Pumped Laser Performance of Er Doped NaY(WO4)2 Disordered Laser Crystals

Undoped and Er-doped NaY(WO4)2 disordered single crystals have been grown by the Czochralski technique. The specific heat and thermal conductivity (κ) of these crystals have been characterized from T = 4 K to 700 K and 360 K, respectively. It is shown that κ exhibits anisotropy characteristic of single crystals as well as a κ(T) behavior observed in glasses, with a saturation mean free phonon path of 3.6 Å and 4.5 Å for propagation along a and c crystal axes, respectively. The relative energy positions and irreducible representations of Stark Er3+ levels up to 4G7/2 multiplet have been determined by the combination of experimental low (<10 K) temperature optical absorption and photoluminescence measurements and simulations with a single-electron Hamiltonian including both free-ion and crystal field interactions. Absorption, emission and gain cross sections of the 4I13/2↔4I15/2 laser related transition have been determined at 77 K. The 4I13/2 Er3+ lifetime (τ) was measured in the temperature range of 77–300 K, and was found to change from τ (77K) ≈ 4.5 ms to τ (300K) ≈ 3.5 ms. Laser operation is demonstrated at 77 K and 300 K by resonantly pumping the 4I13/2 multiplet at λ≈1500 nm with a broadband (FWHM≈20 nm) diode laser source perfectly matching the 77 K crystal 4I15/2 → 4I13/2 absorption profile. At 77 K as much as 5.5 W of output power were obtained in π-polarized configuration with a slope efficiency versus absorbed pump power of 57%, the free running laser wavelength in air was λ≈1611 nm with the laser output bandwidth of 3.5 nm. The laser emission was tunable over 30.7 nm, from 1590.7 nm to 1621.4 nm, for the same π-polarized configuration.

Efficient infrared (≈1.9-2.0 μm) laser operation in color-defect-free Tm:NaGd(MoO4)2 crystal

Color-defect-free 5 at.% Tm:NaGd(MoO4)2 crystals have been grown in a Na2MoO4/Na2Mo2O7 flux. Using a hemispherical optical cavity and pumping at λ = 794.5 nm with a Ti-sapphire laser, up to 850 mW of output power at λ ≈ 1900 nm was obtained at 300 K with an output coupler transmission of 8%. In the cw regime, the slope efficiency versus absorbed power was η = 45% and the pump power laser threshold was ≈180 mW. The laser was tunable from 1875 to 1975 nm and the emission had a FWHM bandwidth ≈20 nm, indicating the potential for ultrashort laser pulse generation.