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

7 pages, 13 figures, 3 tables.-- PACS: 42.55.Rz; 42.60.By; 42.60.FcContinuous 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 1.8 W at 974 nm, a maximum output power of 650 mW was achieved at 1029.6 nm. 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 1010 to 1055 nm. Pulses as short as 90 fs with an average power of 50 mW were generated by passive mode locking at a repetition rate of 95 MHz. 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 5–300 K temperature range and the optical properties of the host at room temperature.This work was supported by Projects Nos. NMP3-CT- 2003-505580 (EU), MAT2004-21113E, and MAT2005-6354- C03-01 (Spain). A.G. (FPU2003-018), X.H. (JC12006-4015-2459) and X.M. (EX2004-1294) are supported by grants from the Spanish government. X.M. additionally acknowledges support from the European Science Foundation.Peer reviewe

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

7 pages, 13 figures, 3 tables.-- PACS: 42.55.Rz; 42.60.By; 42.60.FcContinuous 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 1.8 W at 974 nm, a maximum output power of 650 mW was achieved at 1029.6 nm. 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 1010 to 1055 nm. Pulses as short as 90 fs with an average power of 50 mW were generated by passive mode locking at a repetition rate of 95 MHz. 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 5–300 K temperature range and the optical properties of the host at room temperature.This work was supported by Projects Nos. NMP3-CT- 2003-505580 (EU), MAT2004-21113E, and MAT2005-6354- C03-01 (Spain). A.G. (FPU2003-018), X.H. (JC12006-4015-2459) and X.M. (EX2004-1294) are supported by grants from the Spanish government. X.M. additionally acknowledges support from the European Science Foundation.Peer reviewe

Growth, spectroscopy, and tunable laser operation of the disordered crystal LiGd(MoO4)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.This work was supported by the projects DT-CRYS or NMP3-CT-2003-505580 (European Union) and MAT 2005-6354-C03-01 and CAM-MAT-434-2004 (Spain). M. Rico (EX2003-0784) and X. Han (SB2003-0232) acknowledge the Education and Science Ministry of Spain for financial support.Peer reviewe

Tunable laser operation of ytterbium in disordered single crystals of Yb:NaGd(WO4)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.EU Project DT-CRYS. MAT2002-4605-C05-05. Dr. M. Rico thanks the Universities and Education Secretary of State and the European Social Fund for financial support.Peer reviewe

Continuous wave and tunable laser operation of Yb3+ in disordered NaLa(MoO4)2

Continuous-wave Yb3+ laser operation is studied in single crystals of disordered NaLa(MoO4)2 at room temperature. The sample used was grown by the Czochralski technique and incorporates an Yb ion density of 3.1×1020 cm-3. The effect of the Yb concentration on some of the crystal properties is described as well as the spectroscopic Yb3+ properties at 5 K. Maximum slope efficiencies of about 40% for π and 38% for σ polarization were obtained under Ti:sapphire laser pumping near 976 nm, respectively. The maximum output power for the π polarization was 400 mW at 1039.5 nm, the threshold in this case amounted to 240 mW (absorbed pump power). The laser emission was tunable between 1016 and 1064 nm with a Lyot filter. Lasing was also realized by pumping with a fiber-coupled diode laser module. Maximum output power of 900 mW at 1035 nm was achieved in this case for the π polarization and the threshold was 280 mW. The results, in terms of output power and tunability, are superior in comparison to all previous reports on Yb-doped disordered double tungstate or molybdate crystals and represent a significant improvement in comparison to earlier experiments with low-doped Yb:NaLa(MoO4)2.This work was supported by the projects DT-CRYS, NMP3-CT-2003-505580 (EU), MAT 2002-4605-C05-05 and CAM-MAT-434-2004 (Spain). Dr. M. Rico thanks the Education and Culture Ministry of Spain for financial support.Peer reviewe

Spectroscopy and efficient laser operation near 1.95 μm 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 1799 to 2026 nm. The maximum output power exceeded 0.5 W 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 (I-4) 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.This work was supported by Project No. MAT2005-6354-C03-01 (Spain). J. M. Cano-Torres, X. Han, and M. Rico were supported by the Spanish Science and Education Ministry through I3P-BPD2005, Juan de la Cierva, and Ramón y Cajal grants, respectively.Peer reviewe

Structural, spectroscopic, and tunable laser properties of Yb3+-doped NaGd(WO4)2

Single crystals of Yb3+-doped NaGd(WO4)2 with up to 20 mol % ytterbium content have been grown by the Czochralski technique in air or in N-2+O-2 atmosphere and cooled to room temperature at different rates (4-250 degrees C/h). Only the noncentrosymmetric tetragonal space group I-4 accounts for all reflections observed in the single crystal x-ray diffraction analysis. The distortion of this symmetry with respect to the centrosymmetric tetragonal space group I4(1)/a is much lower for crystals cooled at a fast rate. Na+, Gd3+, and Yb3+ ions share the two nonequivalent 2b and 2d sites of the I-4 structure, but Yb3+ (and Gd3+) ions are found preferentially in the 2b site. Optical spectroscopy at low (5 K) temperature provides additional evidence of the existence of these two sites contributing to the line broadening. The comparison with the F-2(7/2)(n) and F-2(5/2)(n(')) Stark energy levels calculated using the crystallographic Yb-O bond distances allows to correlate the experimental optical bands with the 2b and 2d sites. As a novel uniaxial laser host for Yb3+, NaGd(WO4)2 is characterized also with respect to its transparency, band-edge, refractive indices, and main optical phonons. Continuous-wave Yb3+-laser operation is studied at room temperature both under Ti:sapphire and diode laser pumping. A maximum slope efficiency of 77% with respect to the absorbed power is achieved for the pi polarization by Ti:sapphire laser pumping in a three-mirror cavity with Brewster geometry. The emission is tunable in the 1014-1079 nm spectral range with an intracavity Lyot filter. Passive mode locking of this laser produces 120 fs long pulses at 1037.5 nm with an average power of 360 mW at approximate to 97 MHz repetition rate. Using uncoated samples of Yb:NaGd(WO4)2 at normal incidence in simple two-mirror cavities, output powers as high as 1.45 W and slope efficiencies as high as 51% are achieved with different diode laser pump sources.Projects DT-CRYS or NMP3-CT-2003-505580 (EU), MAT2005-6354-C03-01 (Spain), and BMBF 13N8382 (Germany). M.R. thanks the Education and Science Ministry of Spain for financial support (EX2003-0784).Peer reviewe

Continuous-wave diode-pumped operation of an Yb:NaLa(WO4)2 laser at room temperature

Room-temperature continuous-wave (cw) laser operation is demonstrated with the newly developed Yb:NaLa(WO4)2 disordered crystal by end-pumping with a fiber-coupled diode laser. A maximum output power of 330 mW is obtained with an optical efficiency of 4.9% and a slope efficiency of 6.3% with respect to the incident pump power. The efficiencies in terms of the absorbed pump power are roughly three times higher. Sellmeier dispersion curves for the ordinary and extraordinary refractive indices of the NaLa(WO4)2 host are reported along with crystallographic and spectroscopic properties related to the Yb3+-doping.We acknowledge financial support through Projects MAT 2002-4605-C05-05, CAM-MAT- 434-2004 (Spain), and NMP3-CT-2003-505580 (EU Project DT-CRYS). Dr. M. Rico thanks the Education and Culture Ministry of Spain for financial support.Peer reviewe

Growth and continuous-wave laser operation of disordered crystals of Yb3+:NaLa(WO4)2 and Yb3+:NaLa(MoO4)2

Single crystals of disordered NaLa(WO4)2 and NaLa(MoO4)2 doped with Yb3+ are grown by the Czochralski method from the melt. Continuous-wave laser operation with Ti:sapphire laser pumping is demonstrated at room temperature without special cooling. Tunability from 1017 to 1057 nm and from 1015 to 1053 nm is achieved for Yb:NaLa(WO4)2 and Yb:NaLa(MoO4)2, respectively. A maximum output power of 205 mW is obtained with Yb:NaLa(WO4)2.We acknowledge financial support through Projects MAT2002-4605-C05-05 and CAM-MAT-434-2004 (Spain) and DT-CRYS, NMP3-CT-2003-505580 (EU).Peer reviewe

Continuous-wave laser operation of disordered double tungstate and molybdate crystals doped with ytterbium

Several ytterbium doped disordered doubles tungstate and molybdate crystals, NaGd(WO4)2, NaLa(WO4)2, NaLa(MoO4)2 and LiGd(MoO4)2, were grown with sufficient Yb-doping and optical quality. The crystal field splitting of the Yb3+ multiplets and the lifetimes are similar to the biaxial monoclinic double tungstates but the peak absorption cross sections are roughly one order of magnitude lower. Room temperature cw laser operation was achieved under Ti:sapphire and diode laser pumping. The polarization dependence of the laser emission and possible power scaling were studied. The slope efficiency achieved with the best sample, Yb:LiGd(MoO4)2, was 64.5%. The maximum output power obtained was 900 mW for Yb:NaLa(MoO4)2 pumped in the absorption maximum. The laser tunability was studied with an intracavity Lyot filter and the tuning ranges (FWHM up to 33 nm) achieved indicate interesting potential for mode-locked femtosecond operation.This work was supported by the European Commission under Project DT-CRYS (STRP-505580-1). We acknowledge also financial support through Projects MAT 2002-4605-C05-05, CAM-MAT-434-2004 (Spain), and the Education and Science Ministry of Spain (M. Rico: EX2003-0784, X. Han: SB2003-0232).Peer reviewe