Del Mar Photonics - Newsletter Fall 2010 - Newsletter Winter 2010

Single-Wall Carbon Nanotubes

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Saturable absorber relies on carbon nanotubes
John Wallace

A saturable absorber is a nonlinear optical material that becomes more transparent as the intensity of light falling upon it increases. Passive saturable absorbers can be integrated into laser systems to provide modelocking and into fiberoptic systems for passive optical regeneration. The traditional saturable absorber is a multiple-quantum-well (MQW) structure that requires expensive equipment for fabrication—cleanroom-housed metal-oxide chemical-vapor deposition or similar approaches to create the structure itself, and ion implantation to reduce the device's saturation recovery time from the nanosecond to the more practical picosecond range.

Researchers at Alnair Labs (Saitama-ken, Japan), the National Institute of Advanced Industrial Science and Technology (Ibaraki, Japan), Tokyo Metropolitan University (Tokyo, Japan), and the Research Center for Advanced Science and Technology Tokyo, Japan) have created a saturable absorber from a layer of single-walled carbon nanotubes sandwiched between two pieces of glass, termed a saturable absorber incorporating nanotubes (SAINT). The fabrication process is simple, consisting of spraying nanotubes onto glass. Because carbon nanotubes are chemically stable, no hermetic sealing is required. The optical damage threshold of the device is higher than that of a MQW saturable absorber; in addition, a SAINT works in transmission—an easier-to-work-with mode of operation than the reflective mode required for a MQW device.

The nanotubes themselves are synthesized by ablating a metal-catalyzed carbon target with a Nd:YAG laser in 500 Torr of argon gas. The resulting tubes, with a mean diameter of 1.1 nm, are dispersed in ethanol and sprayed onto 1-mm-thick substrates with an airbrush (see figure). The researchers used the SAINTs for two purposes: a noise-suppressing saturable absorber for 1550-nm light, and a modelocked fiber laser operating in the same 1550-nm spectral region.

Single-walled carbon nanotubes are imaged by an atomic-force microscope (left) and a transmission electron microscope (right). When sprayed onto a glass substrate, these nanotubes exhibit saturable absorption of light, a property useful in fiberoptic systems for noise suppression and laser modelocking.
Click here to enlarge image

The light source for the saturable-absorber setup was a fiber laser producing 1-ps pulse bunches (of about 120 pulses at a time) at an 80-GHz repetition rate. A fiber collimator and an aspheric lens brought the light to a focus on the SAINT. Varying the spot size by shifting the nanotube sample along the optical axis varied the intensity of light falling on the carbon-nanotube film. At a maximum peak intensity of 5.8 MW/cm2, the device reached a transmission of almost 69%, whereas transmission dropped to about 63% at lower powers. Spectral measurements indicate an inhomogeneously broadened absorption that responds on a 1-ps timescale. The performance of this first SAINT device is still far from its full potential, the researchers note.
Two configurations

Modelocking a fiber laser is ordinarily done with a semiconductor saturable absorber mirror (SESAM). For their modelocking experiment using a SAINT instead of a SESAM, the researchers put together a fiber laser in two different configurations, one with a ring geometry and the other of linear orientation. The erbium-doped ring laser was backward pumped with a 980-nm laser diode, with two optical isolators ensuring operation in one direction only. The SAINT and associated optics were simply inserted in a break in the ring—a geometry impossible with an ordinary reflective SESAM.

The ring laser began to modelock at a pump power of 18 mW, which could then be backed off to 14 mW, with the laser operating at 6.1 MHz in single-pulse mode (higher pump powers resulted in multiple-pulse operation at harmonics of 6.1 MHz). The resulting soliton pulses had a full-width half-maximum (FWHM) width of 1.1 ps, and were somewhat chirped—though the chirping could be reduced with the use of low-dispersion fiber. When the SAINT was removed from the laser cavity, all modelocking stopped, even at high pump powers.

The linear version of the modelocked fiber laser produced nonsoliton pulses at a repetition rate of 9.85 MHz, a FWHM width of 318 fs, a 3-dB spectral width of 13.6 nm, and an average power of almost 1 mW. "We believe this is the first demonstration of using carbon nanotubes for practical applications in the field of applied optics," said Sze Set, general manager of research and development at Alnair Labs, who noted that there was great interest in this material at this year's Optical Fiber Communications Conference (Atlanta, GA; March 23–28).
 

Del Mar Photonics is involved in research of CNTs, graphene nanoplatelets and graphene materials, develops advanced multifunctional materials for variety of applications as well as research instrumentation for characterization of the above.

We currently we can offer:

1) Graphene nanoplatelets: the stack of multi-layer graphene sheets with high aspect ratio, diameter: 0.5-20 µm, thickness: 5-25 nm.
2) Graphene materials: Graphene Powder, Graphene Oxide Powder, Graphene Suspension.
3) Carbon Nanotubes.
 

Contact our application team to discuss your requirements for high-performance nanocomposite materials, display materials, sensing materials, ultracapacitors, batteries, energy storage and other area to improve electrical, thermal, barrier, or mechanical properties by using low-cost nano-additive.

Graphene nanoplatelets are the stack of multi-layer graphene sheets including platelet morphology, with characteristics as follows:

Request a quote for graphene nanoplatelets

Applications:

The high performance composite additives in PPO, POM, PPS, PC, ABS, PP, PE, PS, Nylon and rubbers.
To improve composite tensile strength, stiffness, corrosion resistance, abrasion resistance and anti-static and lubricant properties.
Mechanical properties modifications.
Conductivity modification.
Fuel tank coating.
In electronic enclosures add electrical conductivity to polymers at low densities of 3 to 5 wt%.
Adding EMI or RFI shielding capabilities to a variety of polymers.
Automotive parts: a composite with nanoplatelets can be painted electrostatically, thereby saving costs.
Aerospace: graphite has long been used in aerospace composites. Nanoplatelets can be combined with other additives to reinforce stiffness, add electrical conductivity, EMI shielding, etc.
Appliances: fortified polymers provide superior thermal and electrical conductivity, thereby saving the costs of separate heat dissipation mechanisms.
Sporting goods: graphite-based composites are stronger and stiffer and lighter than comparable materials.
Coatings and paints: graphene nanoplatelets can be dispersed in a wide variety of materials to add electrical conductivity and surface durability.
Batteries: graphene nanoplatelets increase the effectiveness of Lithium-ion batteries when used to formulate electrodes.
Fuel cells: both bi-polar plate and electrode efficiencies can be improved.

Del Mar Photonics develops advanced instrumentation for research of CNTs, graphene nanoplatelets and graphene materials including lasers for broadband spectroscopy, femtosecond transient absorption and fluorescence measurements.

T&D Scan high resolution Laser Spectrometer based on broadly tunable CW laser
CW single-frequency ring Dye laser
Beacon Femtosecond Optically Gated Fluorescence Kinetic Measurement System
New Hatteras femtosecond transient absorption system
Photon Scanning Tunneling Microscope
 

Graphene is a one-atom-thick planar sheet of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term Graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm,[1][2] who described single-layer carbon foils in 1962.[3] Graphene is most easily visualized as an atomic-scale chicken wire made of carbon atoms and their bonds. The crystalline or "flake" form of graphite consists of many graphene sheets stacked together.
The carbon-carbon bond length in graphene is about 0.142 nm. Graphene sheets stack to form graphite with an interplanar spacing of 0.335 nm, which means that a stack of 3 million sheets would be only one millimeter thick. Graphene is the basic structural element of some carbon allotropes including graphite, charcoal, carbon nanotubes, and fullerenes. It can also be considered as an indefinitely large aromatic molecule, the limiting case of the family of flat polycyclic aromatic hydrocarbons. The Nobel Prize in Physics for 2010 was awarded to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene".[4]

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities. It can be wrapped up into 0D fullerenes, rolled into 1D nanotubes or stacked into 3D graphite.[5]

References

[1] H. P. Boehm, R. Setton, E. Stumpp (1994). "Nomenclature and terminology of graphite intercalation compounds". Pure and Applied Chemistry 66 (9): 1893–1901. doi:10.1351/pac199466091893.
[2] H. C. Schniepp, J.-L. Li, M. J. McAllister, H. Sai, M. Herrera-Alonso, D. H. Adamson, R. K. Prud’homme, R. Car, D. A. Saville, I. A. Aksay (2006). "Functionalized Single Graphene Sheets Derived from Splitting Graphite Oxide". The Journal of Physical Chemistry B 110 (17): 8535–8539. doi:10.1021/jp060936f. PMID 16640401.
[3] H. P. Boehm, A. Clauss, G. O. Fischer, U. Hofmann (1962). "Das Adsorptionsverhalten sehr dünner Kohlenstoffolien". Zeitschrift für anorganische und allgemeine Chemie 316 (3-4): 119–127. doi:10.1002/zaac.19623160303.
[4] Nobel Foundation announcement
[5] Geim, A. K. and Novoselov, K. S. (2007). "The rise of graphene". Nature Materials 6 (3): 183–191. doi:10.1038/nmat1849. PMID 17330084.

Carbon nanotubes (CNTs; also known as buckytubes) are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1,[1] which is significantly larger than any other material. These cylindrical carbon molecules have novel properties which make them potentially useful in many applications in nanotechnology, electronics, optics, and other fields of materials science, as well as potential uses in architectural fields. They may also have applications in the construction of body armor. They exhibit extraordinary strength and unique electrical properties, and are efficient thermal conductors.
Nanotubes are members of the fullerene structural family, which also includes the spherical buckyballs. The ends of a nanotube may be capped with a hemisphere of the buckyball structure. Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers (approximately 1/50,000th of the width of a human hair), while they can be up to 18 centimeters in length (as of 2010).[1] Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs).
Chemical bonding in nanotubes is described by applied quantum chemistry, specifically, orbital hybridization. The chemical bonding of nanotubes is composed entirely of sp2 bonds, similar to those of graphite. These bonds, which are stronger than the sp3 bonds found in diamonds, provide nanotubules with their unique strength. Moreover, nanotubes naturally align themselves into "ropes" held together by Van der Waals forces.

[1] Wang, X.; Li, Q.; Xie, J.; Jin, Z.; Wang, J.; Li, Y.; Jiang, K.; Fan, S. (2009). "Fabrication of Ultralong and Electrically Uniform Single-Walled Carbon Nanotubes on Clean Substrates". Nano Letters 9 (9): 3137–3141. doi:10.1021/nl901260b. PMID 19650638.

Del Mar Photonics, Inc.
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