Browsing by Subject "Graphene electrodes"

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    Broadband terahertz modulators using self-gated graphene capacitors
    (Optical Society of America, 2015) Kakenov, N.; Balci, O.; Polat, E. O.; Altan, H.; Kocabas, C.
    We demonstrate a terahertz intensity modulator using a graphene supercapacitor which consists of two large-area graphene electrodes and an electrolyte medium. The mutual electrolyte gating between the graphene electrodes provides very efficient electrostatic doping with Fermi energies of 1 eV and a charge density of 8 × 1013 cm-2. We show that the graphene supercapacitor yields more than 50% modulation between 0.1 and 1.4 THz with operation voltages less than 3 V. The low insertion losses, high modulation depth over a broad spectrum, and the simplicity of the device structure are the key attributes of graphene supercapacitors for THz applications.
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    Graphene-gold supercapacitor as a voltage controlled saturable absorber for femtosecond pulse generation
    (Optical Society of America, 2016-02) Baylam, I.; Balci, O.; Kakenov, N.; Kocabas, C.; Sennaroglu, A.
    We report, for the first time to the best of our knowledge, use of a graphene-gold supercapacitor as a voltage controlled fast saturable absorber for femtosecond pulse generation. The unique design involving only one graphene electrode lowers the insertion loss of the device, in comparison with capacitor designs with two graphene electrodes. Furthermore, use of the high-dielectric electrolyte allows reversible, adjustable control of the absorption level up to the visible region with low bias voltages of only a few volts (0-2 V). The fast saturable absorber action of the graphene-gold supercapacitor was demonstrated inside a multipass-cavity Cr:forsterite laser to generate nearly transform-limited, sub-100 fs pulses at a pulse repetition rate of 4.51 MHz at 1.24 μm.