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  • Journal article
    Torrisi F, Popa D, Milana S, Jiang Z, Hasan T, Lidorikis E, Ferrari ACet al., 2016,

    Stable, surfactant-free graphene–styrene methylmethacrylate composite for ultrafast lasers

    , Advanced Optical Materials, Vol: 4, Pages: 1088-1097, ISSN: 2195-1071

    Graphene–polymer composites play an increasing role in photonic and optoelectronic applications, from ultrafast pulse generation to solar cells. The fabrication of an optical quality surfactant-free graphene-styrene methyl methacrylate composite, stable to large humidity and temperature ranges is reported. The composite is tailored for photonic applications showing wavelength-independent linear absorption in the visible and near-infrared. When tested in a mode-locked laser, it allows the generation of stable ≈326 fs mode-locked pulses at 1550 nm, unperturbed by environmental conditions. The composite continues to operate as a saturable absorber even under complete water immersion at 60 °C. This confirms its stability against high-temperature and humidity.

  • Journal article
    Fabbro A, Scaini D, León V, Vázquez E, Cellot G, Privitera G, Lombardi L, Torrisi F, Tomarchio F, Bonaccorso F, Bosi S, Ferrari AC, Ballerini L, Prato Met al., 2016,

    Graphene-Based Interfaces Do Not Alter Target Nerve Cells.

    , ACS Nano, Vol: 10, Pages: 615-623, ISSN: 1936-086X

    Neural-interfaces rely on the ability of electrodes to transduce stimuli into electrical patterns delivered to the brain. In addition to sensitivity to the stimuli, stability in the operating conditions and efficient charge transfer to neurons, the electrodes should not alter the physiological properties of the target tissue. Graphene is emerging as a promising material for neuro-interfacing applications, given its outstanding physico-chemical properties. Here, we use graphene-based substrates (GBSs) to interface neuronal growth. We test our GBSs on brain cell cultures by measuring functional and synaptic integrity of the emerging neuronal networks. We show that GBSs are permissive interfaces, even when uncoated by cell adhesion layers, retaining unaltered neuronal signaling properties, thus being suitable for carbon-based neural prosthetic devices.

  • Journal article
    Woodward RI, Howe RCT, Runcorn TH, Hu G, Torrisi F, Kelleher EJR, Hasan Tet al., 2015,

    Wideband saturable absorption in few-layer molybdenum diselenide (MoSe₂) for Q-switching Yb-, Er- and Tm-doped fiber lasers.

    , Opt Express, Vol: 23, Pages: 20051-20061, ISSN: 1094-4087

    We fabricate a free-standing molybdenum diselenide (MoSe2) saturable absorber by embedding liquid-phase exfoliated few-layer MoSe2 flakes into a polymer film. The MoSe2-polymer composite is used to Q-switch fiber lasers based on ytterbium (Yb), erbium (Er) and thulium (Tm) gain fiber, producing trains of microsecond-duration pulses with kilohertz repetition rates at 1060 nm, 1566 nm and 1924 nm, respectively. Such operating wavelengths correspond to sub-bandgap saturable absorption in MoSe2, which is explained in the context of edge-states, building upon studies of other semiconducting transition metal dichalcogenide (TMD)-based saturable absorbers. Our work adds few-layer MoSe2 to the growing catalog of TMDs with remarkable optical properties, which offer new opportunities for photonic devices.

  • Journal article
    Purdie DG, Popa D, Wittwer VJ, Jiang Z, Bonacchini G, Torrisi F, Milana S, Lidorikis E, Ferrari ACet al., 2015,

    Few-cycle pulses from a graphene mode-locked all-fiber laser

    , Applied Physics Letters, Vol: 106, ISSN: 0003-6951

    © 2015 AIP Publishing LLC. We combine a graphene mode-locked oscillator with an external compressor and achieve ∼29-fs pulses with ∼52-mW average power. This is a simple, low-cost, and robust setup, entirely fiber based, with no free-space optics, for applications requiring high temporal resolution.

  • Journal article
    Zhang M, Howe RCT, Woodward RI, Kelleher EJR, Torrisi F, Hu G, Popov SV, Taylor JR, Hasan Tet al., 2015,

    Solution processed MoS2-PVA composite for sub-bandgap mode-locking of a wideband tunable ultrafast Er:fiber laser

    , Nano Research, Vol: 8, Pages: 1522-1534, ISSN: 1998-0000

    We fabricate a free-standing few-layer molybdenum disulfide (MoS2)-polymer composite by liquid phase exfoliation of chemically pristine MoS2 crystals and use this to demonstrate a wideband tunable, ultrafast mode-locked fiber laser. Stable, picosecond pulses, tunable from 1,535 nm to 1,565 nm, are generated, corresponding to photon energies below the MoS2 material bandgap. These results contribute to the growing body of work studying the nonlinear optical properties of transition metal dichalcogenides that present new opportunities for ultrafast photonic applications.

  • Journal article
    Ren Y, Brown G, Mary R, Demetriou G, Popa D, Torrisi F, Ferrari AC, Chen F, Kar AKet al., 2015,

    7.8-GHz Graphene-Based 2-μm Monolithic Waveguide Laser

    , IEEE Journal on Selected Topics in Quantum Electronics, Vol: 21, ISSN: 1077-260X

    © 1995-2012 IEEE. We report a pulsed waveguide laser working at 1944 nm, mode-locked with a saturable absorber consisting of a graphene film deposited on an output coupler mirror. The waveguide is created into a ceramic Thulium-doped Yttrium Aluminium Garnet by ultrafast laser inscription. Q-switched mode-locking is achieved, with 6.5 mW average output power and ∼7.8 GHz pulse rate. This is a convenient, compact, high repetition rate laser for various applications, such as medical diagnostics and spectroscopy.

  • Journal article
    Woodward RI, Howe RCT, Hu G, Torrisi F, Zhang M, Hasan T, Kelleher EJRet al., 2015,

    Few-layer MoS<inf>2</inf> saturable absorbers for short-pulse laser technology: Current status and future perspectives [Invited]

    , Photonics Research, Vol: 3, Pages: A30-A41, ISSN: 2327-9125

    © 2015 Chinese Laser Press. Few-layer molybdenum disulfide (MoS2) is emerging as a promising quasi-two-dimensional material for photonics and optoelectronics, further extending the library of suitable layered nanomaterials with exceptional optical properties for use in saturable absorber devices that enable short-pulse generation in laser systems. In this work, we catalog and review the nonlinear optical properties of few-layer MoS2, summarize recent progress in processing and integration into saturable absorber devices, and comment on the current status and future perspectives of MoS2-based pulsed lasers.

  • Journal article
    Woodward RI, Kelleher EJR, Howe RCT, Hu G, Torrisi F, Hasan T, Popov SV, Taylor JRet al., 2014,

    Tunable Q-switched fiber laser based on saturable edge-state absorption in few-layer molybdenum disulfide (MoS₂)

    , Opt Express, Vol: 22, Pages: 31113-31122, ISSN: 1094-4087

    We fabricate a few-layer molybdenum disulfide (MoS₂) polymer composite saturable absorber by liquid-phase exfoliation, and use this to passively Q-switch an ytterbium-doped fiber laser, tunable from 1030 to 1070 nm. Self-starting Q-switching generates 2.88 μs pulses at 74 kHz repetition rate, with over 100 nJ pulse energy. We propose a mechanism, based on edge states within the bandgap, responsible for the wideband nonlinear optical absorption exhibited by our few-layer MoS₂ sample, despite operating at photon energies lower than the material bandgap.

  • Journal article
    Torrisi F, Coleman JN, 2014,

    Electrifying inks with 2D materials.

    , Nat Nanotechnol, Vol: 9, Pages: 738-739, ISSN: 1748-3395
  • Journal article
    Hasan T, Sun Z, Tan P, Popa D, Flahaut E, Kelleher EJR, Bonaccorso F, Wang F, Jiang Z, Torrisi F, Privitera G, Nicolosi V, Ferrari ACet al., 2014,

    Double-wall carbon nanotubes for wide-band, ultrafast pulse generation.

    , ACS Nano, Vol: 8, Pages: 4836-4847, ISSN: 1936-086X

    We demonstrate wide-band ultrafast optical pulse generation at 1, 1.5, and 2 μm using a single-polymer composite saturable absorber based on double-wall carbon nanotubes (DWNTs). The freestanding optical quality polymer composite is prepared from nanotubes dispersed in water with poly(vinyl alcohol) as the host matrix. The composite is then integrated into ytterbium-, erbium-, and thulium-doped fiber laser cavities. Using this single DWNT-polymer composite, we achieve 4.85 ps, 532 fs, and 1.6 ps mode-locked pulses at 1066, 1559, and 1883 nm, respectively, highlighting the potential of DWNTs for wide-band ultrafast photonics.

  • Journal article
    Purdie D, Popa D, Wittwer VJ, Ziang Z, Torrisi F, Ferrari ACet al., 2014,

    Sub-50 fs compressed pulses from a graphene-mode locked fiber laser

    , Optics InfoBase Conference Papers, ISSN: 2162-2701

    We demonstrate a graphene mode-locked fiber laser system generating 42 fs pulses with 53mW output power, ideal for high temporal resolution applications. © 2014 Optical Society of America.

  • Conference paper
    Woodward RI, Kelleher EJR, Runcorn TH, Popov SV, Torrisi F, Howe RCT, Hasan Tet al., 2014,

    Q-switched fiber laser with MoS<inf>2</inf> saturable absorber

    A MoS2-based saturable absorber is fabricated using wet chemistry techniques. We use it to passively Q-switch a fiber laser at 1068 nm. © 2014 Optical Society of America.

  • Conference paper
    Thomas S, Cole M, De Luca A, Torrisi F, Ferrari AC, Udrea F, Gardner JWet al., 2014,

    Graphene-coated Rayleigh SAW resonators for NO <inf>2</inf> detection

    , Pages: 999-1002, ISSN: 1877-7058

    © 2014 Published by Elsevier Ltd. This paper describes the development of a novel low-cost Rayleigh Surface Acoustic Wave Resonator (SAWR) device coated with a graphene layer that is capable of detecting PPM levels of NO 2 in air. The sensor comprises two 262 MHz ST-cut quartz based Rayleigh SAWRs arranged in a dual oscillator configuration; where one resonator is coated with gas-sensitive graphene, and the other left uncoated to act as a reference. An array of NMP-dispersed exfoliated reduced graphene oxide dots was deposited in the active area inside the SAWR IDTs by a non-contacting, micro ink-jet printing system. An automated Mass Flow Controller system has been developed that delivers gases to the SAWR sensors with circuitry for excitation, amplification, buffering and signal read-out. This SAW-based graphene sensor has sensitivity to NO 2 of ca. 25 Hz/ppm and could be implemented in a low-power low-cost gas sensor.

  • Journal article
    Jiang Z, Bonacchini GE, Popa D, Torrisi F, Ott AK, Wittwer VJ, Purdie D, Ferrari ACet al., 2014,

    Graphene saturable absorber power scaling laser

    , Optics InfoBase Conference Papers, ISSN: 2162-2701

    A solution-processed graphene-film coated on a fiber-based connector is used for stable, mode-locked femtosecond-duration pulses with 16mW average output power. © 2014 OSA.

  • Journal article
    Jiang Z, Bonacchini GE, Popa D, Torrisi F, Ott AK, Wittwer VJ, Purdie D, Ferrari ACet al., 2014,

    Graphene saturable absorber power scaling laser

    , Optics InfoBase Conference Papers, ISSN: 2162-2701

    A solution-processed graphene-film coated on a fiber-based connector is used for stable, mode-locked femtosecond-duration pulses with 16mW average output power. © 2014 Optical Society of America.

  • Conference paper
    Jiang Z, Bonacchini GE, Popa D, Torrisi F, Ott AK, Wittwer VJ, Purdie D, Ferrari ACet al., 2014,

    Graphene saturable absorber power scaling laser

    © 2014 Optical Society of America. A solution-processed graphene-film coated on a fiber-based connector is used for stable, mode-locked femtosecond-duration pulses with 16 mW average output power.

  • Conference paper
    Jiang Z, Bonacchini GE, Popa D, Torrisi F, Ott AK, Wittwer VJ, Purdie D, Ferrari ACet al., 2014,

    Graphene saturable absorber power scaling laser

    , ISSN: 2162-2701

    A solution-processed graphene-film coated on a fiber-based connector is used for stable, mode-locked femtosecond-duration pulses with 16mW average output power. © 2014 Optical Society of America.

  • Conference paper
    Milne WI, Hu G, Howe RCT, Ferrari AC, Torrisi F, Hasan Tet al., 2014,

    Graphene for Plastic electronics

    , Pages: 368-369

    © 2014 ITE and SID. This paper will begin with a description of the liquid phase exfoliation method of graphene production. The remainder of the talk will concentrate on our work on the application of graphene to plastic electronics, including its use as a transparent conductor for transparent pianos and flexible smart windows.

  • Conference paper
    Zhang M, Kelleher EJR, Runcorn TH, Popa D, Torrisi F, Ferrari AC, Popov SV, Taylor JRet al., 2014,

    Synchronously coupled fiber lasers and sum frequency generation using graphene composites

    Graphene mode-locked and self-sychronized fiber lasers are used for sum- frequency mixing in a graphene-polymer composite.

  • Conference paper
    Woodward RI, Kelleher EJR, Runcorn TH, Popov SV, Torrisi F, Howe RCT, Hasan Tet al., 2014,

    Q-switched fiber laser with MoS<inf>2</inf>saturable absorber

    © 2014 Optical Society of America. A MoS2-based saturable absorber is fabricated using wet chemistry techniques. We use it to passively Q-switch a fiber laser at 1068 nm.

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