Xavier Mateos

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.

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}

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

: Tunable and Femtosecond Mode-Locked Laser Operation

The crystal structure of monoclinic KYb(WO4)2 (KYbW) crystals has been refined (in space group C2/c) at room temperature by using single-crystal X-ray diffraction data. KYbW undoped crystals were grown by the TSSG (top-seeded-solution growth) slow-cooling method. The crystals show {110}, {\bar{1}11}, {010} and {310} faces, which basically define their habit. The linear thermal expansion tensor has been determined and the principal axis with maximum thermal expansion (\alpha ^{\,\prime}_{33} = 16.68 × 10−6 K−1), {\bf X}^{\,\prime}_{3}, was located 12° from the c axis. Its principal {\bf X}^{\,\prime}_{1}, {\bf X}^{\,\prime}_{2} and {\bf X}^{\,\prime}_{3} axes are [302], [010] and [106] directions, respectively, in the crystallographic system. The optical tensor has been studied at λ = 632.8 nm at room temperature; two principal axes, Ng and Nm, are located in the ac plane, while the other, Np, is parallel to [010]. The principal axis with maximum refractive index (ng = 2.45), Ng, was located 19° from the c axis.

Efficient 2-

We demonstrate passive mode locking based on the novel monoclinic double tungstate crystal Yb:KLu(WO4)2. We report the shortest pulses ever produced with an Yb-doped tungstate laser using a semiconductor saturable absorber. A pulse duration of 81 fs has been achieved for an average power of 70 mW at 1046 nm. We compare the performance of the polarization oriented parallel to the Nm- and Np-crystallo-optic axes. Results in the femtosecond and picosecond regime are presented applying either Ti:sapphire or diode laser pumping. The great potential of Yb:KLu(WO4)2 as an active medium for ultrashort pulses is demonstrated for the first time, to our knowledge.

mu

We report on the room-temperature spectroscopic properties and continuous-wave laser operation of a new Yb:LuVO4 crystal. The peak absorption cross section for the pi-polarization is 8.42 x 10(-20) cm2 at 985 nm, and the stimulated emission cross section at 1020 nm is 1.03 x 10(-20) cm2. An output power of 0.36 W at 1041 nm was obtained with a slope efficiency of 47% by use of Ti:sapphire laser pumping. With diode pumping the output power reached 1.05 W at the highest available incident pump power of 6.8 W.

m Continuous-Wave Laser Oscillation of Tm

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.

^3 +

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.

:KLu(WO

The strongly anisotropic monoclinic double tungstate crystal KLu(WO/sub 4/)/sub 2/ was doped with Yb/sup 3+/ ions and shown to be a highly efficient active laser medium in the 1-/spl mu/m spectral range for continuous-wave room-temperature operation, very suitable for pumping with InGaAs laser diodes.