Abstract

Titanium-doped Al₂O₃ (Ti:sapphire) laser can be directly pumped by recently developed green and blue indium gallium nitride (InGaN) laser diodes (LDs), and mode-locking operations of the laser with these pump sources have already been reported from several groups. Rohrbacher et al. achieved an average output power of 460 mW using two 2.9-W LDs at 450 nm, and a pulse width of 82 fs was obtained by semiconductor saturable absorber mirror (SESAM) mode-locking [1]. However, the 450-nm pumping has been reported to induce an absorption loss in Ti:sapphire crystals, called pump-induced loss, by Roth et al. According to their qualitative experiment, the pump-induced loss was not observed when pump wavelength was longer than 456 nm [2]. A pumping at green wavelength was more efficient than the 450-nm pumping due to not only the lack of the pump-induced loss but also the higher Stokes and absorption efficiencies. However, the available output power from a single green LD (~520 nm) is lower than that at 450-nm. Sawai et al. demonstrated the first green-diode-pumped Ti:sapphire laser [3], and recently, Gürel et al. reported a successful power scaling resulting 650-mW output power in continuous-wave (CW) operation, and an average output power of 450 mW with a pulse width of 39 fs by Kerr-lens mode-locking, using two overdriven 520-nm LDs [4]. Toward further power scaling, we investigated the characteristics of Ti:sapphire laser pumped by different wavelength.

© 2017 IEEE