Showing papers by "Uwe Griebner published in 2006"
TL;DR: In this article, continuous-wave Yb 3+ -laser operation was studied at room temperature both under Ti:sapphire and diode laser pumping, and a maximum slope efficiency of 77% with respect to the absorbed power was achieved for the polarization by Ti:Sapphire laser pumping in a three-mirror cavity with Brewster geometry.
Abstract: the two nonequivalent 2b and 2d sites of the I4 ¯ structure, but Yb 3+ and Gd 3+ ions are found preferentially in the 2b site. Optical spectroscopy at low 5K temperature provides additional evidence of the existence of these two sites contributing to the line broadening. The comparison with the 2 F7/2n and 2 F5/2n 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 Yb 3+ , NaGdWO42 is characterized also with respect to its transparency, band-edge, refractive indices, and main optical phonons. Continuous-wave Yb 3+ -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 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 97 MHz repetition rate. Using uncoated samples of Yb: NaGdWO42 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.
136 citations
TL;DR: High-quality monoclinic KY(WO4)2 optical waveguides were grown by liquid-phase epitaxy, and laser operation of an Yb-doped KY( WO4), and continuous-wave laser emission near 1 microm was achieved with both surface and buried planar waveguide.
Abstract: High-quality monoclinic $KY(WO_{4})_{2}$ optical waveguides were grown by liquid-phase epitaxy, and laser operation of an Yb-doped $KY(WO_{4})_{2}$ waveguide was demonstrated for the first time to our knowledge. Continuous-wave laser emission near 1 μm 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%.
133 citations
TL;DR: In this article, a monoclinic double tungstate thulium host was directly compared to KGd(WO4)2 and exhibited superior performance in the 2mum range.
Abstract: Monoclinic crystals of Tm-doped KLu(WO4)2 were grown with high crystalline quality for several dopant concentrations. The relevant spectroscopic properties for the 3 F4rarr3H6 laser transition (cross sections, lifetime) were measured at room temperature. Laser oscillation in the 2-mum range was obtained both with Ti:sapphire and diode laser pumping near 800 nm using different setups. The maximum output powers achieved were 1.4 and 4 W, respectively, and the corresponding slope efficiencies with respect to the absorbed power were 60% and 69%, respectively. The novel monoclinic double tungstate thulium host KLu(WO4)2 was directly compared to KGd(WO4)2 and exhibited superior performance. The two laser polarization configurations for Tm:KLu(WO4)2 ,E//Nm and E//Np, were also compared under identical conditions with pumping by the polarized Ti:sapphire laser. Tuning was studied for both of them using an intracavity Lyot filter and the tuning range achieved was from 1800 to 1987 nm. In the case of no polarization selective cavity elements the diode-pumped Tm:KLu(WO4 )2 laser naturally selected the E//Nm polarization
100 citations
TL;DR: In this paper, a Tm3+-doped crystalline material was used to obtain an output power as high as 300mW in the cw regime with Tm laser operating at room temperature, either with Ti-sapphire or diode laser pumping.
Abstract: 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.
61 citations
TL;DR: In this article, single crystals of Yb3+-doped monoclinic potassium lutetium tungstate were grown with several dopant concentrations (0.5%, 5% and 10% in the solution).
60 citations
TL;DR: An efficient and compact diode-pumped continuous-wave Yb:GdVO4 laser is demonstrated, generating an output power of 4.0 W with an optical conversion efficiency of 61% and a slope efficiency as high as 78%.
Abstract: An efficient and compact diode-pumped continuous-wave Yb:GdVO4 laser is demonstrated, generating an output power of 4.0 W with an optical conversion efficiency of 61% and a slope efficiency as high as 78%. With increasing pump power the polarization of the laser output changes from sigma to pi, while in a certain intermediate power range the two polarization states coexist with different emission wavelengths.
59 citations
TL;DR: In this article, the disordered crystal LiGd0.936Yb0.064(MoO4)2 was grown with high optical quality by the flux method using Li2MoO 4 as a solvent.
Abstract: 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.
51 citations
TL;DR: In this article, the laser performance of Yb:KGW under end-pumping with high-power diode bars was investigated, and the pump was delivered through an optical fiber yielding a symmetric but unpromising result.
Abstract: The laser performance of Yb:KGW under end-pumping with high-power diode bars has been investigated. In one configuration, the pump is delivered through an optical fiber yielding a symmetric but unp ...
40 citations
TL;DR: What the authors believe to be the shortest pulses directly generated with an Yb-doped crystalline laser using a semiconductor saturable absorber are demonstrated.
Abstract: Passive mode locking of the ytterbium doped orthovanadate crystal Yb:LuVO4 is reported for the first time. We demonstrate what we believe to be the shortest pulses directly generated with an Yb-doped crystalline laser using a semiconductor saturable absorber. The pulses at 1036 nm have a duration as short as 58 fs for an average power of 85 mW.
39 citations
TL;DR: There is sizable optical bistability in the operation of a continuous-wave diode-pumped Yb:LuVO(4) laser, as a result of the resonant reabsorption losses in the laser crystal which increase with the temperature.
Abstract: We report on sizable optical bistability in the operation of a continuous-wave diode-pumped Yb:LuVO(4) laser, as a result of the resonant reabsorption losses in the laser crystal which increase with the temperature. Significant intensity fluctuations have been observed in a small operational region near the critical point.
34 citations
01 Jan 2006
TL;DR: In this paper, a monoclinic double tungstate thulium host KLu(WO ) was directly compared to KGd (WO) and exhibited superior performance.
Abstract: Monoclinic crystals of Tm-doped KLu(WO ) were grown with high crystalline quality for several dopant concentra- tions. The relevant spectroscopic properties for the F H laser transition (cross sections, lifetime) were measured at room temperature. Laser oscillation in the 2- m range was obtained both with Ti:sapphire and diode laser pumping near 800 nm using different setups. The maximum output powers achieved were 1.4 and 4 W, respectively, and the corresponding slope efficiencies with respect to the absorbed power were 60% and 69%, respectively. The novel monoclinic double tungstate thulium host KLu(WO ) was directly compared to KGd(WO ) and exhibited superior performance. The two laser polarization con- figurations for Tm:KLu(WO ) and , were also compared under identical conditions with pumping by the polar- ized Ti:sapphire laser. Tuning was studied for both of them using an intracavity Lyot filter and the tuning range achieved was from 1800 to 1987 nm. In the case of no polarization selective cavity elements the diode-pumped Tm:KLu(WO ) laser naturally selected the polarization.
TL;DR: In this paper, the spectral tuning of the exciton resonance of a surface quantum well saturable absorber mirror was investigated for the generation of sub-picosecond pulses, employing an optically pumped semiconductor disk laser in the 1μm spectral range.
Abstract: The authors investigate the spectral tuning of the exciton resonance of a surface quantum well saturable absorber mirror for the generation of subpicosecond pulses, employing an optically pumped semiconductor disk laser in the 1μm spectral range. The all-semiconductor laser generates transform-limited pulses as short as 590fs at a 3GHz repetition rate and an output power of 30mW. The pulse duration of the mode-locked laser was supported by the fast relaxation time of the saturable absorber of 1.0ps.
TL;DR: In this article, the first time to our knowledge, laser oscillation of Tm:LuVO4 at room temperature with both Ti:sapphire and diode laser pumping, and tunable operation from 1839 to 1952 nm.
Abstract: We demonstrate for the first time to our knowledge laser oscillation of Tm:LuVO4 at room temperature with both Ti:sapphire and diode laser pumping, and tunable operation from 1839 to 1952 nm. Spectroscopic studies indicate higher gain cross section for the σ-polarization as observed in the laser experiments. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: Several ytterbium doped disordered disordered doubles tungstate and molybdate crystals were grown with sufficient Yb-doping and optical quality as mentioned in this paper, and the crystal field splitting of the Yb 3+ 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.
Abstract: Several ytterbium doped disordered doubles tungstate and molybdate crystals, NaGd(WO 4 ) 2 , NaLa(WO 4 ) 2 , NaLa(MoO 4 ) 2 and LiGd(MoO 4 ) 2 , were grown with sufficient Yb-doping and optical quality. The crystal field splitting of the Yb 3+ 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(MoO 4 ) 2 , was 64.5%. The maximum output power obtained was 900 mW for Yb:NaLa(MoO 4 ) 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.
21 May 2006
TL;DR: In this article, a 12.4 W of output power with optical-to-optical conversion efficiency of 47% and slope efficiency of 74% is demonstrated in Yb:KGW laser end-pumped with high-power diode bars.
Abstract: The generation of 12.4 W of output power with optical-to-optical conversion efficiency of 47% and slope efficiency of 74% is demonstrated in Yb:KGW laser end-pumped with high-power diode bars. Thermal-lensing and laser tuning has been investigated.
TL;DR: In this article, a study of different gain section designs in nonresonantly optically pumped vertically emitting semiconductor disk lasers (SCDLs) is presented, and clear superiority of structures with barriers based on graded-gap layers is demonstrated.
Abstract: Results of a study of different gain section designs in nonresonantly optically pumped vertically emitting semiconductor disk lasers (SCDLs) are presented. Clear superiority of structures with barriers based on graded-gap layers is demonstrated. This finding is assigned to the lack of absorption saturation within the barriers caused by the efficient carrier collection capabilities of graded structures compared to ungraded ones. Transient photoluminescence experiments providing direct access to the carrier transfer from the barrier to the quantum-well active region confirm this explanation. Consequently, the authors propose graded designs for SCDLs.
05 May 2006
TL;DR: In this paper, the authors present the properties and present laser results obtained recently with Yb-doped sesquioxide crystals in the continuous-wave (cw) and mode-locked (picosecond and femtosecond) regimes using both Ti:sapphire and diode-laser pumping.
Abstract: Among the crystalline rare earth laser hosts the isotropic sesquioxides Sc 2 O 3 , Y 2 O 3 , and Lu 2 O 3 (cubic bixbyite structure) are known for their superior thermo-mechanical properties. Their thermal conductivity considerably exceeds that of Y 3 Al 5 O 12 (YAG). Their low phonon energy ensures large energy storage times by minimizing non-radiative relaxation processes. Yb-doped sesquioxides exhibit somewhat broader absorption and emission bandwidths than Yb:YAG which is advantageous for uncritical diode laser pumping and short pulse generation. The splitting of the lower Yb 3+ manifold is also larger which is important in the quasi-four-level operation scheme. Solid solutions with the isostructural Yb 2 O 3 are possible but the observed strong lifetime quenching makes the sesquioxide hosts more suitable for laser geometries that profit from relatively low Yb concentrations. Lu 2 O 3 is the host whose thermal conductivity is least affected by Yb-doping. The high melting point (above 2400°C) makes it difficult to grow the sesquioxides from the melt. Recently, the use of the heat-exchanger-method (HEM) allowed to considerably enhance the optical quality of the grown crystals and the available single crystal size. Here we review the properties and present laser results obtained recently with Yb-doped sesquioxide crystals in the continuous-wave (cw) and mode-locked (picosecond and femtosecond) regimes using both Ti:sapphire and diode-laser pumping. In the cw regime optical-to-optical efficiency of 62.2% and slope efficiency of 72.7% were reached with Yb:Sc 2 O 3 operating at 1041.6 nm. Passive mode-locking of both Yb:Sc 2 O 3 and Yb:Lu 2 O 3 was achieved by semiconductor saturable absorber mirrors. Pulse durations of the order of 200 fs were obtained with intracavity dispersion compensation.
TL;DR: In this paper, a 10% Yb-doped monoclinic KLu(WO4)2 epitaxy was used for continuous-wave and mode-locked laser operation with Ti:sapphire and diodelaser pumping.
Abstract: Epitaxial layers of up to 50% Yb-doped monoclinic KLu(WO4)2 could be successfully grown on passive KLu(WO4)2 substrates. These composite samples were characterized and continuous-wave and mode-locked laser operation was achieved with Ti:sapphire and diodelaser pumping. A 10% Yb-doped epitaxy provided an output power exceeding 500 mW at 1030 nm and a maximum slope efficiency of 66% with Ti:sapphire laser pumping. A 50% Yb-doped epitaxy exhibited serious thermal problems without special cooling and rather limited cw performance. Quasi-cw operation provided in this case an average output power of 43 mW at 1032 nm for a 10% duty cycle. More than 100 mW cw could be generated at 1030 nm also with diode-pumping of the 10% Yb-doped KLu(WO4)2 epitaxy. Pulses as short as 114 fs were generated at 1030 nm with this same sample under Ti:sapphire laser pumping in a laser mode-locked by a saturable absorber mirror.
21 May 2006
TL;DR: In this article, the authors demonstrate output powers exceeding 4 W with continuous-wave, diode-pumped Yb:TVO 4 (T=Y, Gd, and Lu) lasers operated at room temperature.
Abstract: We demonstrate output powers exceeding 4 W with continuous-wave, diode-pumped Yb:TVO 4 (T=Y, Gd, and Lu) lasers operated at room temperature. The three orthovanadate hosts are compared in longitudinal and thin-disk pump geometries.
21 May 2006
TL;DR: In this paper, the authors discuss carefully characterized semiconductor disk lasers with high spatial and spectral homogeneity, exhibiting 23% conversion efficiency and a 540mW output power for cw operation.
Abstract: We discuss carefully characterized semiconductor disk lasers with high spatial and spectral homogeneity, exhibiting 23% conversion efficiency and a 540-mW output power for cw operation. Passive mode-locking with 1.5-ps pulse duration is also demonstrated.
21 May 2006
TL;DR: In this article, a Tm:KLu(WO 4 ) 2 laser near 2 μm under Ti:sapphire and diode laser pumping was obtained with a maximum output power of 1.4 and 4 W and slope efficiencies of 60 and 69%.
Abstract: Maximum output powers of 1.4 and 4 W and slope efficiencies of 60 and 69% were obtained with a Tm:KLu(WO 4 ) 2 laser near 2 μm under Ti:sapphire and diode laser pumping, respectively.
21 May 2006
TL;DR: In this article, a disordered uniaxial crystal Yb:LiGd(MoO 4 ) 2 has been used for diode-pumping, achieving an output power of 470 mW, slope efficiency of 64.5% and tunability between 1016 and 1049 nm.
Abstract: Output power of 470 mW, slope efficiency of 64.5% and tunability between 1016 and 1049 nm are achieved with the novel disordered uniaxial crystal Yb:LiGd(MoO 4 ) 2 . Both possible polarizations are compared and diode-pumping is also demonstrated.