The present invention describes a mode locking semiconductor disk laser (SDL). The laser comprises a resonator terminated by first and second mirrors (6,7) and folded by a third mirror. The third mirror comprising a semiconductor disk laser (8) suitable for generating a resonator field comprising a predetermined central wavelength A O while the second mirror comprising an intensity saturable mirror (7) suitable for mode locking the resonator field at the predetermined wavelength. The reflectivity of the of the resonator at the central wavelength A O is reduced by shifting the reflectivity profiles of the first and or second mirrors to wavelength shorter than the predetermined wavelength so as to suppress gain at wavelengths longer than the central wavelength A O . By mismatching the reflectivity profile (32) of the second mirror (7) to that of the desired output wavelength (3) provides a stable mode locked laser with significantly reduced noise. The SDL may comprise a DBR with a reflectivity profile (1) having a peak wavelength corresponding to the laser emission (3). The gain medium comprises a RPG structure of the active region resulting in a Fabry-Perot with a FSR as indicated by the corresponding reflectivity profile (2). The peak reflection of the DBR of the saturable absorber mirror may be shifted towards shorter wavelengths with respect to the laser emission by an amount corresponding to one half to one FSR of said RPG active region.