Abstract
Semiconductor saturable absorber mirrors (SESAMs) using quantum dot (QD) absorbers exhibit a larger design freedom than standard quantum well absorbers. The additional parameter of the dot density in combination with the field enhancement allows for an independent control of saturation fluence and modulation depth. We present the first detailed study of the effect of QD growth parameters and post growth annealing on the macroscopic optical SESAM parameters, measuring both nonlinear reflectivity and recombination dynamics. We studied a set of self-assembled InAs QD-SESAMs optimized for an operation wavelength around 960 nm with varying dot density and growth temperature. We confirm that the modulation depth is controlled by the dot density. We present design guidelines for QD-SESAMs with low saturation fluence and fast recovery, which are for example important for modelocking of vertical external cavity surface emitting lasers (VECSELs).
Highlights
Since the early 90’s, picosecond and femtosecond lasers have made a large impact both in fundamental science and industrial applications
We present design guidelines for quantum dot (QD)-semiconductor saturable absorber mirror (SESAM) with low saturation fluence and fast recovery, which are for example important for modelocking of vertical external cavity surface emitting lasers (VECSELs)
We studied the effect of dot density and post-growth annealing on quantum dot SESAMs
Summary
Since the early 90’s, picosecond and femtosecond lasers have made a large impact both in fundamental science and industrial applications. Semiconductor absorber materials are ideally suited to initiate and stabilize pulse formation because they cover a broad wavelength range from the visible to the infrared, and can be manufactured to provide sufficiently fast recovery time in the picosecond or even femtosecond regime Their integration into a mirror structure provides a large design freedom to tune the relevant absorber parameters, which is important to overcome modelocking instabilities such as Q-switched modelocking (QML) [3]. Rafailov et al reported fast recovery dynamics, which can be beneficial for achieving shorter pulse durations [7] and pulse durations as short as 114 fs have been shown [8] Another advantage of the QD-SESAM is the lower density of states and the additional parameter of the dot density which allow for low saturation fluence at moderate modulation depth. We discuss design guidelines for combining low saturation fluence, optimum modulation depth, and fast recovery
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