Femtosecond pulses with the interpulse periods that are twice the cavity round-trip time accompanied by two decentered TEM<sub>00</sub> beam spots have been obtained with a self-mode-locked Ti:sapphire laser. By use of two photodiodes to measure the beam spots separately, I found that the pulses occurred at alternate spots on successive round trips. The observation can be explained by the presence of a double-pass cavity mode that reproduces itself after two return transits in an effective confocal resonator along an off-axis path rather than by total mode locking.
© 2001 Optical Society of America
(140.3410) Lasers and laser optics : Laser resonators
(140.3590) Lasers and laser optics : Lasers, titanium
(140.4050) Lasers and laser optics : Mode-locked lasers
(140.7090) Lasers and laser optics : Ultrafast lasers
Hsiao-Hua Wu, "Interpulse period doubling in a self-mode-locked Ti:sapphire laser," J. Opt. Soc. Am. B 18, 1597-1600 (2001)