Fabricating graphite nano-sheet powder by slow electrochemical exfoliation of large-scale graphite foil as a mode-locker for fiber lasers

Abstract

Without the need of single-layer graphene, the graphite nano-sheet powder electrochemically exfoliated from graphite foil can also be employed as a stable saturable absorber and mode-locker for fiber lasers. High-quality graphite nano-sheets containing few graphene layers can be obtained by slow electrochemical exfoliation without the need of post annealing procedure. With reducing the electrochemical exfoliation bias of the graphite foil based anode from + 6 and + 3 volts, the electrochemically exfoliated graphite nano-sheets reveals a decreased D-band intensity in Raman scattering spectrum, and the 2D-band intensity is concurrently enlarged by two times to support the improved quality with suppressed oxidation during the exfoliation reaction. The X-ray photoelectron spectroscopy also confirms the suppression of the C-O bonds in the graphite nano-sheets obtained with decreasing the exfoliation bias. After centrifugation, the average diameter of the exfoliated graphite nano-sheets extracted from the acetone solution is shrunk from 7 μm to 100 nm as the anode bias decreases from 6 to 3 volts. Both the quality and size distribution of the graphite nano-sheets are improved with such slow but refined electrochemical exfoliation. In application, the graphite nano-sheets obtained at different exfoliation bias show relatively stable saturable absorption and passive mode-locking performance in Erbium doped fiber lasers (EDFLs). Benefiting from the advantages of high-gain and strong pulse compression in the EDFL, the graphite nano-sheets with different modulation depths only behave as a mode-locking starter and show trivial influence to the pulse shortening in the mode-locked EDFL, indicating that the strong soliton compression mechanism dominates the generation of 430-450 fs pulsewidth in the EDFL passively mode-locked by graphite nano-sheets.