21-fs Diode-Pumped Kerr-Lens Mode-Locked Yb:(Y,Sc)₂O₃ Sesquioxide Laser

Ytterbium (Yb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>) doped cubic sesquioxides, Yb:RE<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>, where RE = Lu, Y, and Sc, are of particular interest for high-power, sub-100-fs ~1 μm solid-state lasers due to their excellent thermo-mechanical properties, high doping levels, broad gain profiles, and strong crystal fields leading to large Stark splitting of Yb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>+ multiplets [1]. Yb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>- doped “mixed” (solid-solution) sesquioxides exhibit significant inhomogeneous spectral line broadening due to compositional disorder, making them highly promising for the generation and amplification of ultrashort laser pulses. Moreover, some “mixed” sesquioxides have significantly reduced melting temperatures compared to their parent compounds, enabling growth via the well-established Czochralski method with high optical quality and large sizes [2]. Recently, we reported on the crystal growth, spectroscopy, and laser operation of a 3 at.% Yb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup>-doped “mixed” sesquioxide single-crystal, Yb:(Y<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</inf>SC<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l/2</inf>)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>, shortly Yb:(Y,Sc)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>. Mode-locked (ML) by a commercially available SESAM, the Yb:(Y,Sc)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> laser generated 48 fs pulses at 1056.4 nm with an average output power of 45 mW [3]. In this work, we demonstrate the first sub-30 fs pulse generation from this diode-pumped Yb:(Y,Sc)<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> laser via soft-aperture Kerr-lens mode-locking (KLM).