Tunable Graphene/Quantum‐Dot Van der Waals Heterostructures’ Saturable Absorber Plane Arrays by Two‐Step Femtosecond and Nanosecond Laser Postprocessing

Abstract

Van der Waals heterostructures (vdWHs) based on graphene/III−V semiconductors have attracted considerable interest. Although diverse proof‐of‐concepts are demonstrated, it is a challenge to make a tunable array device using such vdWHs that severely limit its practical applications. Herein, a controllable and reliable two‐step femtosecond (fs) and nanosecond (ns) pulsed laser postprocessing method to enhance the material quality is described–especially the nonlinear optical (NLO) characteristics of such vdWHs, the significantly improved light absorption capability, and the obviously reduced saturable fluence (SF) are simultaneously obtained compared with the as‐grown device, allowing to construct a stable and high‐performance ultrafast fiber laser. In addition, benefiting from the unique selective‐area annealing nature of laser postprocessing, a saturable absorber (SA) plane array device by the same original vdWHs but under various fs and ns laser annealing treatments is realized, exhibiting large tuning ranges of modulation depth (from 1.6 to 11.2%) and SF (from 13.7 to 1.1 MW cm−2), paving a new way to fabricate an array device using vdWHs.

Keywords

• laser annealing
• nonlinear optical characteristics
• quantum dots
• semiconductor saturable absorber mirrors
• van der Waals heterostructures