Uwe Griebner

Yb-doped KY(WO4)2 planar waveguide laser

High-quality monoclinic KY(WO4)2 optical waveguides were grown by liquid-phase epitaxy, and laser operation of an Yb-doped KY(WO4)2 waveguide was demonstrated for the first time to our knowledge. Continuous-wave laser emission near 1 microm 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%.

Passive mode locking of Yb:KLuW using a single-walled carbon nanotube saturable absorber

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.

Passive mode-locking of a Tm-doped bulk laser near 2 µm using a carbon nanotube saturable absorber

Stable and self-starting mode-locking of a Tm:KLu(WO(4))(2) crystal laser is demonstrated using a transmission-type single-walled carbon nanotube (SWCNT) based saturable absorber (SA). These experiments in the 2 microm regime utilize the E11 transition of the SWCNTs for nonlinear saturable absorption. The recovery time of the SWCNT-SA is measured by pump-probe measurements as approximately 1.2 ps. The mode-locked laser delivers approximately 10 ps pulses near 1.95 microm with a maximum output power of up to 240 mW at 126 MHz repetition rate.

Double Tungstate Lasers: From Bulk Toward On-Chip Integrated Waveguide Devices

It has been recognized that the monoclinic double tungstates KY(WO4)2, KGd(WO4)2, and KLu(WO4)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.

Fabrication and characterization of ultrafast carbon nanotube saturable absorbers for solid-state laser mode locking near 1μm

Transmitting and reflecting ultrafast saturable absorbers based on single-walled carbon nanotubes are developed that are applicable for stable mode locking of bulk solid-state lasers operating near 1μm. For fabrication of these saturable absorbers, relatively simple spin coating and spray methods are employed. Parameters important for stable mode locking, such as transient nonlinear absorption, saturation fluence, and recovery time, are investigated by nonlinear transmission and time-resolved pump-probe measurements near 1μm. Typical modulation depths and recovery times amount to ∼0.21%–0.25% and <1ps, respectively.

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}

We demonstrate the operation of a low threshold femtosecond Yb:KYW laser, using a saturable absorber mirror for passive mode-locking and a high brightness laser diode as pumping source. Fourier-limited pulses with a duration of 101 fs are achieved at an output power of 100 mW. The performance of the Yb:KYW laser was also compared to that of Yb:KGW.

: Tunable and Femtosecond Mode-Locked Laser Operation

We report what we believe to be the first passive mode-locking of Cr:forsterite laser using a single-walled carbon nanotube saturable absorber (SWCNT-SA). The dispersion-compensated Cr:forsterite laser in a self-starting configuration produces nearly Fourier transform-limited pulses as short as 120 fs near 1.25 microm. The maximum average output power of 202 mW obtained with a 5% output coupler at a repetition rate of 79.1 MHz represents, to the best of our knowledge, the highest power level ever reported for SWCNT-SA mode locking of solid-state lasers.

Passively mode-locked Yb:KYWlaser pumped by a tapered diode laser.

Monoclinic crystals of Tm-doped KLu(WO₄)₂ were grown with high crystalline quality for several dopant concentrations. The relevant spectroscopic properties for the ³F₄rarr³H₆ 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//N_m and E//N_p, 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//N_m polarization

Mode-locked self-starting Cr:forsterite laser using a single-walled carbon nanotube saturable absorber

Pure and doped nanocrystalline ZnO films of 0.1–1.0 μm thickness were prepared by spray pyrolysis techniques. Structural properties of these thin films were investigated by electron microscopy, force microscopy, x-ray diffractometry, ellipsometry, and optical spectroscopy. Using Ti:sapphire laser pulses, the second-harmonic efficiency of the films was measured. A correlation between measured efficiency and the grain shape in the polycrystalline layers is reported. Moreover, measurements of the angular dependence of the second-harmonic intensity are indicative of the dominant role of bulk effects over surface effects for the second-harmonic generation in such films.