Abstract
We present passive mode locking of a vertical external-cavity surface-emitting laser (VECSEL) in the red spectral range with quantum dots (QDs) as active material in the gain and in the absorber structure. Both semiconductor samples are fabricated by metal-organic vapor-phase epitaxy (MOVPE) in a near-anti-resonant design. A vshaped cavity is used to tightly focus onto the semiconductor saturable absorber mirror (SESAM), producing pulses with a duration of less than 1 ps and a repetition rate of 852MHz. In order to increase the field enhancement inside the absorber structure, some SESAM samples were additionally coated with a fused silica layer. The pulse duration as well as the mode locking stability were investigated for different thicknesses of the SiO 2 layer. The most stable mode locking operation is observed for a 97 nm SiO 2 layer, while the disadvantage of this overall near-resonant SESAM structure is an increased pulse duration of around 2 ps. Due to the improved stability, the transmission of the outcoupling mirror could be increased resulting in an average output power of 10mW at an emission wavelength of 651 nm.
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