Ultrafast Nonlinear Optical Properties of a Graphene Saturable Mirror in the 2 μm Wavelength Region

Mid-infrared ultrafast lasers have emerged as a promising platform for both science and industry because of their inherent high raw power and eye-safe spectrum. 2D nanostructures such as graphene have emerged as promising photonic materials for laser mode-locking to generate ultrashort pulses. However, there are still many unanswered questions about graphene's key advantages to be practical devices, especially over the matured semiconductor saturable absorber mirror (SESAM). In this work, we conducted systematic comparisons on the nonlinear optical properties of graphene and that of a commercial SESAM at 2 mu m wavelength. Our results showed that graphene has significant advantages over the commercial SESAM, exhibiting similar to 28% less absorptive cross-section ratio of excited-state to ground-state and similar to 50 times faster relaxation time. This implies that graphene can be exploited as a better mode-locker than the current commercial SESAM for high power, high repetition rate and ultrafast mid-infrared laser sources.