We demonstrate a diode-pumped SESAM mode-locked Yb:(Y,Gd)AlO3 laser delivering soliton pulses as short as 28-fs at 1063 nm with an average output power of 21 mW. The maximum average output power is scaled to 135 mW for a pulse duration of 37 fs.
We report on the continuous-wave (CW) and Kerr-lens mode-locked (KLM) operation of an ytterbium (Yb3+) doped orthorhombic calcium rare-earth borate Yb:Ca3Gd2(BO3)4 (Yb:GdCB) disordered crystal. A high quality 10 at.% Yb:GdCB crystal was grown by the Czochralski method. An X-shaped astigmatically compensated linear cavity was employed for evaluating the CW and KLM laser performance of an a-cut (sp. gr. Pnma) Yb:GdCB crystal. Pumping with a single-transverse mode, fiber-coupled diode laser at 976 nm, a maximum CW output power of 548 mW was obtained at 1049 nm with a slope efficiency of 67.8% and a linear laser polarization (E || b). A broad wavelength tuning range of ~88 nm (1001 – 1089 nm) was achieved in the CW regime. Stable KLM operation was initiated and stabilized by a semiconductor saturable absorber mirror (SESAM). Nearly Fourier-transform-limited pulses as short as 33 fs were generated at a central wavelength of 1055.3 nm with an average output power of 98 mW for a pulse repetition rate of ~67.3 MHz.
We report on the Czochralski growth, polarized optical spectroscopy, thermal lensing and diode-pumped laser operation of a Yb3+-doped monoclinic “mixed” calcium rare-earth oxoborate crystal, Gd0.235Y0.672Yb0.093Ca4O(BO3)3 (Yb:GdYCOB). The absorption, stimulated-emission and gain cross-section spectra are determined for light polarizations E || X, Y, Z. The maximum σSE above the zero-phonon line is 0.61 x 10-20 cm2 at 1022.4 nm (for E || X) and the luminescence lifetime of Yb3+ ions is 2.37 ms. The gain spectra of Yb:GdYCOB extend beyond 1.15 μm. The thermal lens is studied for the three principal cuts, X-cut, Y-cut and Z-cut, and it is found to be positive. A continuous-wave diode-pumped X-cut Yb:GdYCOB laser generates 9.27 W at ~1050 nm with a slope efficiency of 68.2%, linear laser polarization E || X and nearly diffraction-limited beam (M2x,y < 1.16). A continuous wavelength tuning from 1020.9 to 1086.3 nm (a tuning range of ~65 nm) is achieved for the Z-cut crystal and the laser polarization E || X.
We report on efficient mid-IR difference-frequency generation (DFG) at ~8 μm in orientation-patterned GaAs (OPGaAs), by mixing the signal and idler fields inside a nanosecond, singly-resonant, periodically-poled MgO-doped LiNbO3 optical parametric oscillator (OPO). The temperature and spectral acceptance bandwidths as well as the DFG output performance are compared for two OP-GaAs samples with different lengths. Temperature tuning of the DFG is studied by implementing a transversely chirped Volume Bragg Grating (VBG) as one of the OPO cavity mirrors for the signal wave. The maximum DFG average power amounts to 215 mW at 8.15 μm for a pulse repetition rate of 35 kHz. The corresponding overall optical conversion efficiency from 1 to 8 μm is ~1.1%.
The exceptional power scalability of Yb lasers has enabled the development of pulsed optical parametric amplifiers (OPA’s) operating at the short-wave edge of the mid-IR (MIR) with average powers beyond 10 W simultaneously providing peak powers in excess of 1 GW. Further wavelength extension into the longer-wave MIR is enabled by novel wide-bandgap non-oxide nonlinear crystals that can be pumped directly at 1 μm without detrimental one- and twophoton absorption of pump radiation. Eliminating the usual difference frequency generation step in producing MIR pulses above 5 μm could potentially increase the conversion efficiency of parametric down-conversion devices and enable a significant boost in the attainable average and peak power. Despite their utmost importance, material properties related to ultrafast laser-induced damage in nonlinear crystals are rarely investigated in the corresponding laser parameter range. In order to help unravel the complicated interplay of photorefractive effects, thermal lensing, and selffocusing/ defocusing affecting the beam quality and catastrophic breakdown threshold in MIR OPA’s, we present the nonlinear index of refraction at 1 μm of KTiOAsO4, LiGaS2, and BaGa4S7. The reported data provide crucial design parameters for the development of high-average-power MIR OPA’s. As examples, (i) a 100-kHz, 1.55/3.1 μm dual-beam OPA delivering multi-GW peak power in each beam and a total average power of 55 W and (ii) a 100-kHz, sub-100-fs, 1-μm-pumped OPA tunable in the 5.7-10.5-μm range are briefly presented.
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