Andreas Gross

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.

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.

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.

Segmented Growth of Monoclinic Yb:KY(WO 4 ) 2 /KY(WO 4 ) 2 and its Laser Operation

Composite Yb:KY(WO₄)₂ grown on KY(WO₄)₂ substrates by segmented growth showed highly efficient continuous-wave laser operation with slope efficiencies as high as 80% and 375 mW output power was demonstrated.