Fig. 1. Flow chart of preparation of graphene capacitor

Fig. 2. Preparation and characterization of graphene capacitor. (a) Preparation process; (b) operation principle of device；(c) Raman spectrum; (d) transmission spectra

Fig. 3. Electrode structural diagrams of graphene capacitor. (a) Micrographs of ring electrode; (b) simulated electric field intensity diagram

Fig. 4. Photoelectric performances of graphene capacitor. (a) Optical absorption spectra under different gate voltages；(b) capacitance characteristics; (c) band diagram of negative pressure device; (d) band diagram of positive pressure device

Fig. 5. Nonlinear transmission characteristics of graphene device. (a) Nonlinear absorption characteristics of device under different gate voltages; (b) modulation depth versus gate voltage of graphene device

Fig. 6. Experimental layout of passively Q-switched green laser based on graphene device

Fig. 7. Output powers of continuous and pulsed lasers versus absorbed pump power

Fig. 8. Single pulse and pulse sequence (inset) under each gate voltage. (a) 0 V; (b) 60 V

Fig. 9. Pulse duration and repetition rate versus gate voltage

Fig. 10. Laser stability analysis. (a) Output power versus PPLN crystal temperature; (b) time evolution of output power

Fig. 11. Output characteristics of pulsed laser at absorbed pump power of 1.78 W. (a) Laser spectrum and light spot (inset); (b) laser spectrum