Pulses of 55-fs width and 1.2-GHz repetition rate at 1.52 μm are generated from an L-fold cavity Cr<sup>4+</sup>:YAG laser by optimization of the lasing-beam mode inside the gain medium. The pulse width is comparable with that obtained from a standard Z-fold cavity. The pulses are characterized by a second-harmonic-generation frequency-resolved optical gating method. The pulse shape deviates from a sech<sup>2</sup> function because of its broad shoulders. With further miniaturization it should be possible to extend the Cr<sup>4+</sup>:YAG mode-locked operation to multigigahertz rates.
© 2000 Optical Society of America
(060.4230) Fiber optics and optical communications : Multiplexing
(140.3580) Lasers and laser optics : Lasers, solid-state
(140.4050) Lasers and laser optics : Mode-locked lasers
(320.7090) Ultrafast optics : Ultrafast lasers
Tatsuya Tomaru and Hrvoje Petek, "Femtosecond Cr4+:YAG laser with an L-fold cavity operating at a 1.2-GHz repetition rate," Opt. Lett. 25, 584-586 (2000)