Graphene,a two-dimensional carbon atom sheet,has attracted tremendous attention and research interest because of its exceptional physical properties.Graphene has high mobility and optical transparency,in addition to flexibility,robustness and environmental stability.The main focus so far has been on fundamental physics and electronic devices.However,because the linear dispersion of the Dirac electrons enables ultrawideband tunability,we believe its true potential lies in photonics and optoelectronics.In this review,we introduce recent advances in the nonlinear optical properties of graphene-based materials.The rise of graphene in nonlinear optics is shown by several recent results,ranging from saturable absorbers and the four-wave mixing effect to giant two-photon absorption,reverse saturable absorption and optical limiting.The relevant forms of the graphene-based materials include pure graphene,graphene oxide and graphene hybrids.
LIU ZhiBoZHANG XiaoLiangYAN XiaoQingCHEN YongShengTIAN JianGuo
We report a passively Q-switched and mode-locked erbium-doped fiber laser(EDFL) based on PtSe_2, a new two-dimensional material, as a saturable absorber(SA). Self-started Q-switching at 1560 nm in the EDFL was achieved at a threshold pump power of 65 mW, and at the maximum pump power of 450 m W, the maximum single Q-switched pulse energy is 143.2 n J. Due to the polarization-dependent characteristics of the PtSe_2-based SA, the laser can be switched from the Q-switched state to the mode-locked state by adjusting the polarization state. A mode-locked pulse train with a repetition rate of 23.3 MHz and a pulse width of 1.02 ps can be generated when the pump power increases to about 80 m W, and the stable mode-locked state is maintained until the pump power reaches its maximum 450 m W. The maximum single mode-locked pulse energy is0.53 nJ. This is the first time to our knowledge that successful generation of stable Q-switched and mode-locked pulses in an Er-doped fiber laser has been obtained by using PtSe_2 as a saturable absorber.
KANG ZHANGMING FENGYANGYANG RENFANG LIuXINGSHUO CHENJIE YANGXIAO-QING VANFENG SONGJIANGUO TIAN
Pump-probe differential reflection and transmission spectroscopy is a very effective tool to study the nonequilibrium carrier dynamics of graphene. The reported sign of differential reflection from graphene is not explicitly explained and not consistent. Here, we study the differential reflection and transmission signals of graphene on a dielectric substrate. The results reveal the sign of differential reflection changes with the incident direction of the probe beam with respect to the substrate. The obtained theory can be applied to predict the differential signals of other two-dimensional materials placed on various dielectric substrates.
