A review on the latest developments on graphene, written from the perspective of a chemist, is presented. The role of chemistry in bringing graphene research to the next level is discussed.

The chemistry of graphene

This Review discusses the emerging field of mid-infrared frequency comb generation, including technologies based on novel laser gain media, nonlinear frequency conversion and microresonators, as well as the applications of these combs in precision spectroscopy and direct frequency comb spectroscopy. Laser frequency combs are coherent light sources that emit a broad spectrum of discrete, evenly spaced narrow lines whose absolute frequency can be measured to within the accuracy of an atomic clock. Their development in the near-infrared and visible domains has revolutionized frequency metrology while also providing numerous unexpected opportunities in other fields such as astronomy and attosecond science. Researchers are now exploring how to extend frequency comb techniques to the mid-infrared spectral region. Versatile mid-infrared frequency comb generators based on novel laser gain media, nonlinear frequency conversion or microresonators promise to significantly expand the applications of frequency combs. In particular, novel approaches to molecular spectroscopy in the 'fingerprint region', with dramatically improved precision, sensitivity, recording time and/or spectral bandwidth may lead to new discoveries in the various fields relevant to molecular science.

Mid-infrared frequency combs

Fibre lasers in the mid-infrared regime are useful for a diverse range of fields, including chemical and biomedical sensing, military applications and materials processing. This Review summarizes the different rare-earth cations and host materials used in mid-infrared fibre laser technology, and discusses the future applications and challenges for the field.

Towards high-power mid-infrared emission from a fibre laser

Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Nanotube–Polymer Composites for Ultrafast Photonics

Under strong laser radiation, a Dirac material, the topological insulator (TI) Bi2Te3, exhibits an optical transmittance increase as a result of saturable absorption. Based on an open-aperture Z-scan measurement at 1550 nm, we clearly show that the TI, Bi2Te3 under our investigation, is indeed a very-high-modulation-depth (up to 95%) saturable absorber. Furthermore, a TI based saturable absorber device was fabricated and used as a passive mode locker for ultrafast pulse formation at the telecommunication band. This contribution unambiguously shows that apart from its fantastic electronic property, a TI (Bi2Te3) may also possess attractive optoelectronic property for ultrafast photonics.

Ultra-short pulse generation by a topological insulator based saturable absorber

We report a ring-cavity thulium fiber laser mode locked with a single-wall carbon nanotube absorber used in transmission. A carboxymethyl cellulose polymer film with incorporated carbon nanotubes synthesized by the arc discharge method has an absorption coinciding with in the amplification bandwidth of a Tm-doped fiber. This laser is pumped by an erbium fiber laser at 1.57 μm wavelength and produces a 37 MHz train of mode-locked 1.32 ps pulses at 1.93 μm wavelength with an average output power of 3.4 mW.

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Mode-locked 1.93 μm thulium fiber laser with a carbon nanotube absorber

A mode-locked soliton erbium-doped fiber laser generating 177fs pulses is demonstrated. The laser pumped by a 85mW, 980nm laser diode emits 7mW at 1.56μm at a pulse repetition rate of 50MHz. Passive mode locking is achieved with a saturable absorber made of a high-optical quality film based on cellulose derivative with dispersed carbon single-wall nanotubes. The film is prepared with the original technique by using carbon nanotubes synthesized by the arc-discharge method.

177fs erbium-doped fiber laser mode locked with a cellulose polymer film containing single-wall carbon nanotubes

We studied the ring and linear schemes of erbium-doped fibre lasers in which passive mode locking was achieved with the help of saturable absorbers made of high-optical quality films based on cellulose derivatives with dispersed single-wall carbon nanotubes. The films were prepared by the original method with the use of nanotubes synthesised by the arc discharge method. The films exhibit nonlinear absorption at a wavelength of 1.5 μm. Pulses in the form of optical solitons of duration 1.17 ps at a avelength of 1.56 μm were generated in the ring scheme of the erbium laser. The average output power was 1.1 mW at a pulse repetition rate of 20.5 MHz upon pumping by the 980-nm, 25-mW radiation from a laser diode. The pulse duration in the linear scheme was reduced to 466 fs for the output power up to 4 mW and a pulse repetition rate of 28.5 MHz. The specific feature of these lasers is a low pump threshold in the regime of generation of ultrashort pulses.

https://iopscience.iop.org/article/10.1070/QE2007v037n03ABEH013520/pdf

Self-mode-locking in erbium-doped fibre lasers with saturable polymer film absorbers containing single-wall carbon nanotubes synthesised by the arc discharge method

An optical clock based on an Er3+ fiber femtosecond laser and a two-mode He–Ne/CH4 optical frequency standard (λ=3.39 μm) is realized. Difference-frequency generation is used to down convert the 1.5-μm frequency comb of the Er3+ femtosecond laser to the 3.4-μm range. The generated infrared comb overlaps with the He–Ne/CH4 laser wavelength and does not depend on the carrier–envelope offset frequency of the 1.5-μm comb. In this way a direct phase-coherent connection between the optical frequency of the He–Ne/CH4 standard and the radio frequency pulse repetition rate of the fiber laser is established. The stability of the optical clock is measured against a commercial hydrogen maser. The measured relative instability is 1×10−12 at 1 s and for averaging times less than 50 s it is determined by the microwave standard, while for longer times a drift of the He–Ne/CH4 optical standard is dominant.

Femtosecond fiber laser based methane optical clock

In this letter, we report on a particularly strong optical nonlinearity at the nanometer scale in aluminum. A strong optical nonlinearity of the third order was demonstrated on a single nanoslit. Single nanoslits of different aspect ratio were excited by a laser pulse (120 fs) at the wavelength 1.5 μm, leading predominantly to third-harmonic generation (THG). It has been shown that strong surface plasmon resonance in a nanoslit allows the realization of an effective nanolocalized source of third-harmonic radiation. We show also that a nanoslit in a metal film has a significant advantage in nonlinear processes over its Babinet complementary nanostructure (nanorod): the effective abstraction of heat in a film with a slit makes it possible to use much higher laser radiation intensities.

https://iopscience.iop.org/article/10.1088/1612-2011/10/7/075901/pdf

A. V. Tausenev

Papers

Mode-locked 1.93 μm thulium fiber laser with a carbon nanotube absorber

177fs erbium-doped fiber laser mode locked with a cellulose polymer film containing single-wall carbon nanotubes

Self-mode-locking in erbium-doped fibre lasers with saturable polymer film absorbers containing single-wall carbon nanotubes synthesised by the arc discharge method

Femtosecond fiber laser based methane optical clock

Single nano-hole as a new effective nonlinear element for third-harmonic generation