Cankun Zhang

Graphene-Based Fluorescence-Quenching-Related Fermi Level Elevation and Electron-Concentration Surge

Intermolecular p-orbital overlaps in unsaturated π-conjugated systems, such as graphene and fluorescent molecules with aromatic structure, serve as the electron-exchanged path. Using Raman-mapping measurements, we observe that the fluorescence intensity of fluorescein isothiocyanate (FITC) is quenched by graphene, whereas it persists in graphene-absent substrates (SiO2). After identifying a mechanism related to photon-induced electron transfer (PET) that contributes to this fluorescence quenching phenomenon, we validate this mechanism by conducting analyses on Dirac point shifts of FITC-coated graphene. From these shifts, Fermi level elevation and the electron-concentration surge in graphene upon visible-light impingements are acquired. Finally, according to this mechanism, graphene-based biosensors are fabricated to show the sensing capability of measuring fluorescently labeled-biomolecule concentrations.

Passive synchronization of 106- and 153-μm fiber lasers Q-switched by a common graphene SA

We demonstrate the passive synchronization of two large-energy Q-switched all-fiber lasers, operating at 1.06 and 1.53 μm, by sharing a common monolayer graphene Q-switcher. The fiber-compatible Q-switcher is constructed by transferring a monolayer CVD graphene nanosheet onto a fiber ferrule. By exploiting the broadband saturable absorption of graphene and optimizing the cavity designs, both the large-energy Q-switched Yb and Er/Yb double-clad fiber lasers are successfully synchronized. The Q-switching synchronization can be realized in the broad repetition-rate range of 9-20 kHz by adjusting the pump powers of the two lasers. The maximum pulse energies are 5.30 μJ at 1.06 μm and 1.20 μJ at 1.53 μm, respectively, which is, to the best of our knowledge, the largest pulse energy obtained from graphene Q-switched all-fiber laser.