Doping-induced changes in the saturable absorption of monolayer graphene
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Graphene is a broadband, fast saturable absorber well suited for passive mode-locking of lasers. The broadband absorption, ultra-short recovery time, and low cost of graphene absorbers compare favorably with traditional semiconductor saturable absorber mirrors (SESAMs). However, it remains difficult to tailor the parameters of a monolayer graphene absorber such as the modulation depth and the insertion loss; this limits the absorber’s design freedom, which is often required for mode-locking without Q-switching instability. We demonstrate in this work that, by hole-doping graphene chemically to various Fermi levels, the modulation depth and insertion loss are modified. Further control of graphene’s saturable absorption by electric-field gating and its application to active suppression of Q-switching in lasers is discussed.
We deeply appreciate the support from Dr. Kaoru Minoshima, AIST/NMIJ Tsukuba, Japan, who provided us the Er:Yb:glass. We would also like to express our gratitude toward Prof. Markus Raschke for lending us the use of the micro-Raman system and toward Joanna Atkin and Samuel Berweger for lending us their expertise in Raman spectroscopy. This research was supported in part by the NNIN at the Colorado Nanofabrication Laboratory and the National Science Foundation under Grant No. ECS-0335765 and by the Innovative Seed Grant Program at the University of Colorado.
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