Volker Wesemann

Large and stable thickness coupling coefficients of [001]c-oriented KNbO3 and Li-modified (K,Na)NbO3 single crystals

Large thickness coupling factors kT⩽0.7 are measured in both [001]C-oriented (45° cut in the orthorhombic ac plane), monodomain and [001]C-poled, domain-engineered single crystals of KNbO3. kT is extremely stable over a large temperature range, remaining high (⩾0.65) even upon heating and cooling through the orthorhombic-tetragonal phase transition. This is likely related to another finding that spontaneously high kT values (⩽0.68) are observed in as-grown (unpoled), [001]C-cut, polydomain KNbO3 crystals. kT is also stable upon thinning to thicknesses below 60μm, as required for high-frequency applications. Finally, large kT values (⩽0.7) are reported in [001]C-poled, polydomain, Li-doped (K0.5Na0.5)NbO3.

YAl3(BO3)4: a novel NLO crystal for frequency conversion to UV wavelengths

A new family of nonlinear optical (NLO) crystals is presented for the generation of ultraviolet (UV) light by frequency conversion. Included in this family are REAl3(BO3)4 with RE = Y, Lu and other rare earths. Phase matching properties of YAl3(BO3)4 (i.e., YAB) are described in detail.

Diffusion Bonding of Monoclinic Yb:KY(WO4)2/KY(WO4)2 and its Continuous-Wave and Mode-Locked Laser Performance

Diffusion bonding of strongly anisotropic double tungstate crystals with high quality interfaces was successfully implemented. The bonded Yb:KY(WO4)2/KY(WO4)2 composite crystals showed an impressive performance both in the continuous-wave and mode-locked laser regime. More than 800 mW of continuous-wave output power at 1.04 µm and slope efficiencies up to 70% were obtained at room temperature without cooling. In the passively mode-locked regime, pulse durations as short as 66 and 62 fs have been achieved directly from the oscillator and with external compression, respectively.

Characterization and laser performance of a new material: 2 at. % Nd:YAG grown by the Czochralski method

We report on the optical quality and laser performance of Czochralski-grown 2-at. %-doped Nd:YAG. Using a diode pumped laser in an end pumped configuration, we compare the laser performance of this material with the performance of 1-at. %-doped Nd:YAG and 0.7-at. %-doped Nd:YVO4 crystals. Experimental results show the superior performance of 2-at. % Nd:YAG over Nd:YVO4. With a pump power of 25.7 W, a maximum output power of 12.3 W with a slope efficiency of 57% and an optical-to-optical efficiency of 48% were achieved.

Yb:YAl 3 (BO 3 ) 4 as gain material in thin-disk oscillators: demonstration of 109 W of IR output power

The first demonstration of an Yb:YAl3(BO3)4 thin-disk laser is reported. An output power of 109 W with an optical efficiency of 50.2% was achieved in multimode CW-operation which is to the best of our knowledge a significant record performance compared to previous reports on CW-lasers with this material. At a lower power level of 19.3 W the material proved its suitability for efficient operation with an optical efficiency of 60.4%. In fundamental-mode operation the extracted output power was 10.4 W with an optical efficiency of 44.5% and a beam propagation factor M(2) = 1.39. The broad emission bandwidth of the material was confirmed by measuring a continuous wavelength tuning range from 1001 to 1053 nm with a maximum output power of 36 W at 1040 nm.

Segmented grown Yb:KY(WO 4 ) 2 /KY(WO 4 ) 2 for use in continuous-wave and mode-locked lasers

Segmented growth of monoclinic Yb:KY(WO(4))(2) on KY(WO(4))2(2) substrates was successfully implemented and its excellent laser performance demonstrated. High slope efficiencies up to 80% and an output power of 375 mW were achieved under Ti:sapphire laser pumping in the continuous-wave regime. In the passively mode-locked regime, pulses as short as 99 fs with an average output power of 69 mW were obtained.

Second harmonic generation in the new nonlinear optical material BiB/sub 3/O/sub 6/

Summary form only given. The monoclinic BiB/sub 3/O/sub 6/ is a new nonlinear optical material. Recently, large BiB/sub 3/O/sub 6/ crystals have been grown with good optical quality. Meanwhile, the Sellmeier coefficients were published an calculations indicated the suitability for nonlinear applications. We report on an investigation of the properties of this material for frequency doubling (SHG) of e.g. Nd:YAG laser radiation (1064 nm). The 5 mm long crystal used in these investigations was cut in the y-z-plane. The two crystal facets were AR coated for 1064 nm and 532 nm. Important parameters for efficient SHG are the linear losses at 1064 nm and the effective nonlinearity. Both parameters were measured across the crystals aperture (of 3/spl times/3 mm) with a spatial resolution of 120 /spl mu/m. In addition, we determined the temperature and the angular acceptance bandwidth.

Diffusion Bonding of Monoclinic Yb:KY(WO 4 ) 2 /KY(WO 4 ) 2 and Its Continuous-Wave Laser Operation

Diffusion bonding of the strongly anisotropic Yb:KY(WO4)2and KY(WO4)2crystals was successfully demonstrated. Efficient continuous-wave laser operation with slope efficiencies as high as 70% and 811 mW output power was obtained.

109 W Yb:YAl 3 (B0 3 ) 4 thin-disk oscillator

In this contribution, what is believed to be the first demonstration of an Yb:YAl3(BO3)4 (Yb:YAB) thin-disk laser is reported. Due to its broad gain bandwidth of >40 nm (σ- polarization), Yb:YAB offers the potential for generating ultrafast laser pulses with sub-100-fs durations; the thin-disk geometry should allow to scale the average power of such pulses beyond the 100 W range. For these experiments, Yb:YAB boule material with a doping concentration of 12 % was polished to a disk with a diameter of 6.3 mm and a thickness of 250 μm. The thin-disk crystal was glued with its HR coated backside on a copper heat sink. Although the Yb YAB crystal was damaged during the mounting process, an usable optical aperture of the disk of up to 3 mm remained. For this reason pump spot diameters of 2.3 and 2.6 mm were selected for the high power laser experiments. A fiber-coupled laser diode high-power laser operation at a central wavelength of 976 nm emitting up to 1 kW of power was utilized as the pump source. In order to guarantee sufficient pump light absorption, a pump module allowing 24 passes of the pump radiation through the thin-disk was chosen. During laser operation the thin-disk crystal was efficiently cooled by an impingement cooling operated at a water temperature of 15 °C. Prior to the high power experiments a thermal characterization of this thin-disk crystal with a thermal-imaging camera was performed. The temperature of the front side of the crystal was measured both during fluorescence and laser operation. For a pump power density of 2.7 kW/cm2 the maximum surface temperatures was determined to be 71 °C in fluorescence and 56 °C in laser operation. These values confirmed the good suitability of Yb YAB for high-power laser operation in thin-disk configuration.

Mode-locked laser operation of a diffusion-bonded Yb:KY(WO 4 ) 2 /KY(WO 4 ) 2 Crystal

We report the shortest pulses (62 fs) ever produced with an Yb-doped monoclinic double tungstate laser by passive mode-locking of diffusion-bonded Yb:KY(WO₄)₂/KY(WO₄)₂ achieving an average power of 182 mW at 1029 nm.