Since 2000, semiconductor saturable absorber mirrors (SESAMs) have been used to realize mode locking of vertical external-cavity surface-emitting lasers (VECSELs), achieving femtosecond pulse durations, GHZ repetition rates and several Watts of average output power. Despite these excellent results, SESAMs which have to be carefully adjusted to the gain structure can be a limiting factor for the development of a cost-effective pulsed laser system. In recent years, a new concept of VECSEL mode locking, the self-mode locking technique, has been demonstrated. While the mechanism behind this kind of mode locking is not yet fully explained, most publications focus on the effect of Kerr lensing. We present first experiments on SESAM-free mode locking of red-emitting AlGaInP-VECSELs with different cavity geometries based on the assumption of Kerr lensing in the active region. Our semiconductor samples are grown by metal-organic vapor-phase epitaxy with an active region containing GaInP quantum wells embedded in AlGaInP barriers and cladding layers. In order to exploit the effect of Kerr lensing, a slit is placed inside the cavity acting as a hard aperture. When the beam width is confined, pulsed operation is observed by oscilloscope and autocorrelation measurements. Ongoing research is focusing on a detailed characterization of the pulsed laser to improve one's understanding of the obtained SESAM-free mode-locked operation.
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