We report what we believe to be the first demonstration of cw and passively mode-locked Yb 3+ : YAlO 3 (Yb:YAP) laser operation under diode pumping. Spectroscopic properties of a 0.6 at.% Yb 3+ -doped YAP single crystal were investigated. Output power up to 1.2 W with slope efficiency of 64.5% in the cw regime and 225 fs pulse duration with average power of 0.8 W from a mode-locked Yb:YAP laser were demonstrated. OCIS codes: 140.3380, 140.3480, 140.3615, 140.4050, 140.5680. Present widespread use of efficient InGaAs laser diodes and favorable electronic structure of ytterbium ions stimulate interest in Yb 3+ -doped solid-state materials for diode-pumped high-power lasers emitting in the spectral range near 1 m. Broad gain bandwidth of these media has stimulated their applications for generation of ultrashort pulses in modelocked regime.
© 2008 Optical Society of AmericaSo far, the highest average output power of 60 W with ultrashort pulses has been obtained with a thindisk Yb:YAG laser, passively mode-locked with a semiconductor saturable-absorber mirror (SESAM) [1]. The thermal conductivity of YAG is about 13 W / ͑mK͒. However, the emission bandwidth of Yb:YAG limits the pulse duration to only 700-800 fs in a thin-disk laser, or to 340 fs in a bulk laser [2]. Much shorter pulse durations were reported for a number of crystals with broader emission bands, such as Yb-doped YVO 4 [19,20]. It was shown that Yb 3+ ͑15 at.% ͒ : YAP crystal is a potential candidate for compact, efficient thin-chip lasers; in addition, its broad emission band allows the generation of ultrashort pulses. The latest description and analysis of Yb:YAP crystal growth, structural characterization, and spectroscopic properties were published in [21]. In this study, Boulon et al. reported experimental decay-time dependence on Yb 3+ -dopant concentrations, and room-temperature absorption and emission cross section spectra along the a axis were given. Radiative lifetime of an upper-laser level was estimated there to be 0.6 ms, which has a large discrepancy with the decay time published in [19].In our study polarized absorption spectra of Yb 3+ ͑0.6 at.% ͒ : YAP at room temperature were measured by a Varian CARY-5000 spectrophotometer. The content of ytterbium ions in crystal was measured by means of a Tescan VEGA II LMU scanning electron microscope with Oxford INCA Energy 350 energy dispersive x-ray analyzer and was estimated to be 1.17ϫ 10 20 cm −3 . The cross-section spectra for three polarizations are shown in Fig. 1. Strong absorption is found for E ʈ c light polarization. A peak absorption cross-section at 978.2 nm is about 6.6 ϫ 10 −20 cm 2 , however, with comparatively narrow bandwidth of about 4 nm. For a and b polarizations maximal absorption cross sections near 978.5 nm are 0.97ϫ 10 −20 cm 2 and 1.38ϫ 10 −20 cm 2 , respectively. The stimulated emission cross sections are also given in Fig. 1. They were calculated by use of a modified