José María Cano-Torres

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}

Output powers as high as 300mW were obtained at 1925nm in the cw regime with a Tm laser operating at room temperature, either with Ti-sapphire or diode laser pumping, using a new single crystal of NaGd(WO4)2 grown by the Czochralski method and doped with 5mol.% of Tm3+ in the melt. This crystal belongs to the I4¯ tetragonal space group and exhibits a locally disordered structure due to the random occupancy of the same lattice sites by Na and Gd (or Tm) ions. The local disorder results in large bandwidths of the Tm3+ optical transitions (e.g., FWHM≈60cm−1 at 5K for the H63-->F43 transition involved in the laser emission), which allows one to obtain one of the broadest laser tunability ranges, from 1813 to 2025nm(≈17THz), achieved with a Tm3+-doped crystalline material. A detailed characterization of the Tm3+ optical spectroscopy in this novel host was performed at 5 and 300K.

: Tunable and Femtosecond Mode-Locked Laser Operation

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.

Broadly tunable laser operation near 2μm in a locally disordered crystal of Tm 3+ -doped NaGd(WO 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.

Tunable continuous wave and femtosecond mode-locked Yb3+ laser operation in 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.

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

Broadly tunable (1847-2069 nm) continuous-wave laser operation of 4.68 at % Tm-doped NaY(WO4)2disordered crystals is demonstrated. The maximum output power obtained without cooling the sample was 406 mW at a slope efficiency of 39%.

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

CW laser operation of Tm³⁺ in Czochralski-grown disordered NaY(WO₄)₂ crystals is demonstrated. The tunability extends from 1847 to 2069 nm. The maximum slope efficiency and output power amount to ap43% and ap400 mW, respectively.

Tunable, Continuous-Wave near 2-μm Laser Operation of Tm 3+ in NaY(WO 4 ) 2 Single Crystal

The Tm3+ laser efficiency of NaGd(MoO4)2 crystals (η=50.8%, Pout=641mW) grown in Na2MoO4/Na2Mo2O7 flux is larger than that obtained in similar Czochralski-grown crystals annealed to eliminate color centers.

Tunable laser operation of Yb:NaY(MoO 4 ) 2

Broadly tunable (1825-2000 nm) continuous-wave laser operation with maximum output power of 435 mW and slope efficiency of 57.5% is demonstrated for the first time with the disordered Tm:NaLu(WO 4 )2crystal.

Influence of point defects on the laser efficiency of Tm-doped sodium double molybdate crystals

We report now on lasing of Tm³⁺ in the isostructural host NaLa(WO₄)₂, shortly NaLaW, which was grown for the present work by the Czochralski method, with 5 mol % Tm substitution in the melt.