Ultra-short Optical Pulse Generation with Single-layer Graphene

Since the first report of single-layer graphene a few years ago, this material has already proven to possess a great number of interesting properties. One of these properties is its non-linear optical behavior, namely its wavelength-independent saturation of optical absorption. This saturable absorption can be utilized to induce self-amplitude modulation in a laser cavity, thus mode-locking lasers at wavelengths ranging from visible to far-infrared. In addition to the broadband absorption, graphene has an ultrafast relaxation time (∼100 fs) in its carrier-carrier intraband scattering process and a slow relaxation time (∼1 ps) in its carrier-phonon interband scattering process. These two components make graphene excellent for generating self-starting, ultrashort optical pulses in solid-state lasers. Thanks to the development of chemical vapor deposition (CVD) on copper foils, large-area single-layer graphene can be grown and transferred to substrates suitable for optics experiments. Multilayer graphene has been used to mode-lock fiber lasers, 4 and very recently, to generate picosecond pulses in an Nd:YAG ceramics laser. CVD-grown single-layer graphene has also been demonstrated to be able to generate femtosecond pulses in a Cr:forsterite laser. While all these previous experiments used gain media with relatively high gain and high power pump sources,