Ultrashort pulses supported by SESAM absorber

Abstract

We have developed a mode-locked diode-pumped Yb:KYW laser generating nearly band-width limited pulses as short as 101 fs. At 1.1 W absorbed power and 3% transmission output coupler, the laser delivers 150 mW for pulse duration of 110 fs, what corresponds to an efficiency of 14%. It was achieved using semiconductor saturable absorber mirror (SESAM) grown by molecular beam epitaxy. SESAM contains a distributed Bragg reflector (DBR) completed by single quantum well (SQW) playing role of an absorbing layer. The absorbers were crystallized in accordance with the predicted structure parameters under optimised growth conditions. The resonant-like type of structures ensured relatively high enhancement factor due to antireflective properties of SiO2 capping material and a wavelength independence of a group delay dispersion. The optimisation of the growth conditions of both an absorbing layer and DBR structure were widely carried out. Optical reflectance and high resolution X-ray diffraction have been used for characterization and verification of DBR structures. It results in reduction of the nonsaturable absorption in SESAM and self-starting mode-locking of the ultrashort pulses.