Excited-state absorption in the range of pumping and laser efficiency of Cr4+:forsterite

The absorption saturation and the laser efficiency of Cr(4+): forsterite were measured with 1064-nm (E || b), 980-nm (E || c), and 780-nm (E || b) pulsed laser pumping. A slope efficiency of 32% was obtained for the 980-nm (E || c) pump wavelength, where the excited-state absorption losses were shown to be negligible.     

Cr(2+):ZnSe and Co(2+):ZnSe saturable-absorber Q switches for 1.54-mum Er:glass lasers

Passive Q switching of Er:glass lasers has been demonstrated with Cr(2+):ZnSe and Co(2+):ZnSe saturable absorbers. A pulse duration of ~50ns and an output pulse energy of 5 mJ were obtained with both Co:ZnSe and Cr:ZnSe passive shutters. A Q-switched conversion efficiency of as much as 26% was obtained for Cr:ZnSe. Theoretical modeling exhibits satisfactory agreement with experimental data.     

Electrical transport and magnetic ordering in R 2Ti3Ge4 (R=Dy, Ho and Er) compounds

New R ₂Ti₃Ge₄ (R=Dy, Ho and Er) intermetallic compounds have been synthesized and characterized by X-ray diffraction and low temperature ac magnetic susceptibility, electrical resistivity and thermoelectric power measurements were carried out. The compounds crystallize in the parent, Sm₅Ge₄-type orthorhombic structure (space group Pnma) and lanthanide contraction is observed as one moves along the rare-earth series. The changeover from paramagnetic to antiferromagnetic phase happens at low temperatures and the ordering temperature scales with the de Gennes factor. The electrical resistivity is metallic with a negative curvature above 100 K. Thermopower displays a weak maximum at temperatures less than 50 K signifying the possible phonon and magnon drag effects.     

Pulsed laser operation of Y b-dope d KY(WO(4))(2) and KGd(WO(4))(2)

Spectroscopic properties and laser performance of Y b-doped tungstates at pulsed Ti:sapphire laser pumping are reported. Room-temperature lasing near 1025nm is demonstrated in Yb:KY(WO(4))(2) and Yb:KGd(WO(4))(2), with a slope efficiency as great as 86.9%.     

Efficient laser operation and continuous-wave diode pumping of Cr2+:ZnSe single crystals

Efficient continuous-wave laser operation of Cr²⁺:ZnSe was demonstrated with an output power of 1400 mW at an absorbed pump power of 1900 mW from a Tm:YAG laser. Under continuous-wave diode pumping at 1.54 μm an output power of 15 mW was obtained from a Cr⁺²:ZnSe laser. Excited state absorption is shown to be negligible in the pump and laser spectral region. Received: 12 October 2000 / Published online: 30 November 2000     

Soliton blueshift in tapered photonic crystal fibers

We show that solitons undergo a strong blueshift in fibers with a dispersion landscape that varies along the direction of propagation. The experiments are based on a small-core photonic crystal fiber, tapered to have a core diameter that varies continuously along its length, resulting in a zero-dispersion wavelength that moves from 731 nm to 640 nm over the transition. The central wavelength of a soliton translates over 400 nm towards a shorter wavelength. This is accompanied by strong emission of radiation into the UV and IR spectral regions. The experimental results are confirmed by numerical simulation.     

Intensity-driven,laser induced transformation of Ag nanospheres to anisotropic shapes

The shapes of initially spherical Ag nanoparticles in soda-lime glass are persistently changed using fs laser irradiation. With linearly polarized pulses, this shape transformation of the nanoparticles causes optical dichroism of the material. The intensity dependence of this effect is studied comprehensively, addressing the whole intensity range of permanent modifications as well as the influence of the number of laser pulses applied to one spot on the sample. The results are used as basis to develop a complete scenario of the possible mechanisms leading to the laser-induced shape transformation of metallic nanoparticles in glass.     

Elastic properties of the Ta–V system: bcc Ta0.33V0.67 and C15 TaV2

Resonant ultrasound spectroscopy was used to measure the elastic constants of bcc Ta_0.33V_0.67 over the temperature range 3.5–300?K; the results were compared to earlier measurements on C15 TaV₂. The temperature dependence of the polycrystalline shear modulus is completely different in the two phases; that of the bcc phase decreases with temperature whereas that of the C15 phases increases in an anomalous fashion. This difference is consistent with a model involving doubly-degenerate levels at the X point of the Brillouin zone in the C15 phase with the Fermi level lying near the doubly degenerate level. This model accounted for the unusual behaviour of the C15 phase. Debye temperatures were determined from the ultrasonic measurements: 295?K for the C15 phase and 315?K for the bcc phase.     

Femtosecond laser assisted production of dichroitic 3D structures in composite glass containing Ag nanoparticles

Three-dimensional, permanent anisotropic modifications in glass containing spherical Ag nanoparticles are demonstrated using multicolor fs laser irradiation. The method can produce dichroism by deformation of nanoparticles to oblong shapes oriented parallel to the laser polarization. Using samples with a vertical gradient of the fill factor of Ag nanoparticles in the glass substrate and an accordingly inhomogeneous broadening of the surface plasmon band, modifications in various depths can be made using different excitation wavelengths. The induced modifications are reversible: heating to ≈600 °C restores the spherical shape of Ag nanoparticles. This technique could be used in manufacturing of different, 3D, polarization and wavelength selective micro-devices such as polarizers, filters, gratings, display and rewriting optical 3D data storage devices. PACS 78.55.Hx; 78.67.Bf; 78.40.Ha     

Passive Q-switching of 1.44 μm and 1.34 μm diode-pumped Nd:YAG lasers with a V:YAG saturable absorber

Spectroscopic data of a V³⁺:YAG passive Q-switch crystal were measured. The absorption recovery time was determined to be of 37±7 ns and the ground state absorption cross section was estimated to be 0.7×10^-18 cm² at 1.44 μm and 3.5×10^-18 cm² at 1.34 μm. Passively Q-switched operation of diode pumped 1.44 μm and 1.3 μm Nd:YAG lasers was demonstrated using this crystal as saturable absorber. Average output powers of 1.42 W (1.44 μm) and 1.56 W (1.34 μm) and pulse energies of 24 μJ (1.44 μm) and 25 μJ (1.34 μm) were observed, respectively. Received: 19 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +49-40/42838-6281, E-mail: kretschmann@physnet.uni-hamburg.de