Lasers - Page 5

Researchers from the University of Utah developed a new way to develop large arrays of graphene nanoribbons (GNRs), aiming for applications in photodetectors. Their method can directly write a large array of 15nm GNRs on a multilayer epitaxial graphene sheet using Focused Ion Beam (FIB).

The researchers accelerated ga+ ions to 30 keV in vacuum using a FEI Helios NanoLab 650 dual-beam FIB machine. This removed carbon atoms from the graphene sheet with a 1.3 sputtering yield (carbon/Ga+ ratio). This technology can be easily transferred to pattern other graphene nanostructures such as spheres, rings and blocks.

Researchers from Korea developed a new skin cancer photothermal therapy using graphene oxide. The idea is to attach the GO particles to tumor cells, and then shine near-infrared laser light on them. The GO generate heat (and destroy the tumor cells) when exposed to the light, while healthy cells are not effected. Graphene is more efficient than gold for converting the light into heat, and it's also cheaper.

The researcher coupled the graphene with hyaluronic acid, a sugar polymer that is found naturally in skin and is an ingredient in skin care products. The polymer can penetrate the skin’s top layer, and tumor cells are known to express a large number of hyaluronic acid receptors on their surfaces. So this coupling allows the researchers to apply the graphene oxide particles to the skin, avoiding the need to inject them.

Localized hyperthermia is a solid tumor treatment that uses heat (above 43 degrees Celsius) to boost the cytotoxic effects of chemotherapy or radiotherapy and also increases the permeability of tumor cells to drugs. Graphene Oxide is a possible agent because it absorbs light in the near-infrared range.

Researchers from Portugal and Spain studied in vitro laser dosage and cell irradiation exposure time. It was discovered that cell culture temperature (after irradiating cells that had taken up graphene oxide) increases preferentially with laser power rather than with exposure time. Moreover, when the laser power is increased, cell necrosis leads to an increase of cytokine release to the surrounding medium.

Researchers from the Max Planck Institute in Hamburg demonstrated that graphene can be used to emit terahertz laser pulses with long wavelengths. This has been theorized before, but now the researchers actually proved that it can be done. A terahertz direct emission is useful in science but this is the first time that such a laser was developed.

The researcher explain that while graphene band-gap is usually referred to as a zero bandgap, it does have an infinitesimally small bandgap. But the electrons still behave like those of a classic semiconductor, and the population inversion in graphene only lasts for around 100 femtoseconds, less than a trillionth of a second. This means you cannot use graphene for continuous lasers, but it can be used for ultrashort laser pulses.

Researchers from Swinburne University of Technology developed a way to record holographic coding in a graphene oxide polymer composite. This may lead to very safe and secure discs that can retain the holographic information even when broke.

The researchers used an ultrashort laser beam on the graphene oxide polymer, which created a 10 to 100 times increase in the refractive-index (the measure of the bending of light as it passes through a medium) of the graphene oxide along with a decrease in its fluorescence. This offers a new mechanism for multimode optical recording.

Researchers have been trying to create multi-layer graphene flakes in perfect structure. This crease van der Waals heterostructures that can behaves in new ways compared to other graphene structures. But it's difficult to create such a structure.

Researchers from China's Nankai University developed a new method that may enable such structures easily. The new process starts with graphene flakes, then carves them into a any shape desired (using a laser), and then picks them up so they can be transferred elesewhere. This may prove to be an important step towards Van der Waals heterostructures.

Researchers from the University of California, Berkeley created a light-responsive hydrogel made from graphene and elastin-like proteins. When light (a laser) is shining on the gel, it curls inward rapidly. This property is called phototropism - plants use it to orient towards a light source. This material may be useful in robots, drug delivery and synthetic tissue engineering.

The idea behind the new material is that the graphene sheet generates heat when exposed to infrared light,. This causes the proteins to release the water the cling to when not heated.

We already know that laser can be used to produce graphene (see here and here), and in 2010 researchers developed an ultra-fast mode-locked laser using Graphene. A recent research improved their graphene-based laser device to produce a broad spectrum of infrared wavelengths. This may be useful for applications such as fiber optic communications.

The researchers say that their results suggest it will be possible to create graphene-base lasers that emit light over the entire spectrum of visible light.

Researchers from China's National Tsing Hua University found a new use for graphene: photothermal antibacterial therapy. The researchers say that during experiments both gram-positive Staphylococcus aureus and gram-negative Escherichia coli were efficiently captured by glutaraldehyde and concentrated (or immobilized) by the magnetic property of a magnetic reduced graphene oxide functionalized with glutaraldehyde.

The bacteria were rapidly killed by multiple means, including conventional oxidative stress as well as physical piercing and photothermal heating of graphene by near-infrared (NIR) laser irradiation.

Trying to investigate several doping methods for graphene, researchers have found a way to dope graphene with light. This kind of doping is selective and reversibly - meaning that you can change the material attributes using different light colors, angles or polarization. To achieve that doping method, the researchers attached a plasmonic nano antenna to the graphene. The graphene was doped by hot electrons generated from the antenna.

The doping can be controlled by changing the antenna size or the laser's wavelength and power density. n-type graphene provided a larger doping efficiency than p-type graphene.