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Vertical external cavity surface-emitting lasers (VECSELs) have unique properties such as excellent beam quality, high average output power, and high repetition rate. Short pulses from VECSELs, especially picosecond and femtosecond, can be achieved by a passive mode-locking mechanism with a semiconductor saturable absorber mirror (SESAM). We theoretically simulate the pulse evolution dynamics in VECSELs and investigate the influences of different parameters of gain and SESAM on pulse characteristics. To the best of our knowledge, this is the first time that the influences of fast recovery time and two-photon absorption coefficient on pulse characteristics have been studied.

Strain-compensated quantum wells (QWs) could greatly improve the performance of semiconductor disk lasers, such as improving the epitaxy quality of the semiconductor gain chip and obtaining a higher gain. To optimize the output characteristics of the semiconductor gain chip, the strain-compensated thickness, well depth, band energy, emission wavelength, and peak gain versus In and P compositions are investigated in detail. The results show that increasing the P composition of the strain-compensated layer will slightly reduce the emission wavelength, deepen the well depth, and increase the peak gain. But the P composition is not the higher the better. When designing a gain chip, it should have a pre-offset between the emission wavelength of the QWs at room temperature and the target wavelength of the laser at an intense pump, and the pre-offset values of the wavelength should be designed deliberately to guarantee the resonant periodic gain structure working normally when the temperature in the active region approaches the desired value. This theoretical investigation may provide guidance for optimizing the laser performance of semiconductor disk lasers and other QW lasers.

We demonstrated a repetition-rate-tunable second harmonic mode-locked optically pumped semiconductor disk laser (OP-SDL), and the tuning range was from 1.168 GHz to 1.25 GHz. The entire tuning process was continuous, and OP-SDL was always in a mode-locked working state. To the best of our knowledge, this is the first work to obtain intracavity repetition rate tunable second harmonic laser in an OP-SDL. At same time, the repetition rate of fundamental wave can be continuously adjusted from 1.16 GHz to 1.66 GHz. The central wavelengths of the pulse trains were around 971 nm, and the highest repetition rate signal-to-noise ratio was more than 60 dB, indicating that the mode-locked pulses were stable.