SESAM fabrication errors and its influence on ultrafast laser cavity design

Abstract

During mode-locked ultrafast laser experiments, we find that semiconductor saturable absorber mirrors (SESAMs) from the same manufacturing process may, from batch to batch, show different working ranges: pure Q-switching, Q-switched mode-locking, and continuous wave (CW) mode-locking. This is because, in high-volume wafer-scale fabrication, there is typically an estimated 1% error for high-quality molecular beam epitaxy (MBE) growth, which introduces a variation in the parameters of an individual SESAM. In this paper, we will analyze how that 1% error in layer thickness influences the behaviour of SESAMs in three different structures: resonant SESAM, anti-resonant SESAM, and enhanced SESAM. Furthermore, the characteristics of the SESAM will affect the mode-locking dynamic behavior of ultrafast solid state lasers. In the worst case, a SESAM with a fabrication error may prevent the laser cavity from mode-locking. Proper laser cavity design can help to reduce the impact of SESAM fabrication errors on laser performance and maintain the laser in the CW mode-locking range.