via Semiconductor Today.

By embedding a quantum dot within a semiconductor LED structure, researchers in the UK believe that they have created the first electrically driven source of entangled light. Although the most likely beneficiary is quantum computing, entangled light can also be used for quantum imaging, which improves resolution, and for secure communications using quantum cryptography (Nature 465 594).

read more at optics.org.

Quantum dot laser featuring an active layer containing high-density arrays of quantum dots

Fujitsu and the University of Tokyo today announced the world’s first quantum dot laser -based 25 Gbps high-speed data transmission.

via Physorg

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A new device that controls light using an array of tiny gold structures coated with carbon nanotubes has been developed by physicists in the UK and Italy. Based on a “photonic metamaterial”, the devices could find use in lasers and optical communications components.

via physicsworld.com.

The gratings were inscribed in the active fiber using a 193nm excimer laser. Because it induces index grating in the fiber core by a two-photon excitation process, it does not require hydrogenation to photosensitize the fiber. This not only avoids laser efficiency degradation, but also simplifies fabrication.

via SPIE Newsroom.

Diamond is best known for being a prized gem and the hardest cutting element available, but now thanks to research being carried out at Macquarie University it is also proving to be a super efficient laser material.

Associate Professor Richard Mildren and his colleagues at the Macquarie University Photonics Research Centre discovered it was possible to generate a coherent laser beam from man-made diamond in late 2008. They have now demonstrated diamond lasers with efficiency higher than almost all other materials.

“The major achievement is that we are able to use synthetic diamond to create high performing laser devices,” Mildren said. “We are now in good position to explore the highly exotic laser properties of diamond, many of which are not so widely appreciated.

“For example, the speed at which heat travels through diamond is the highest of all known materials, and it is hoped that this property will enable us to simultaneously miniaturise the device and increase the laser beam power to unprecedented levels.”

The diamonds used in the laser research are colourless, approximately eight millimetres long, and weigh a bit less than a carat. They are grown to the researcher's specifications using a process called chemical vapour deposition that essentially creates the crystal lattice carbon by carbon atom and layer by layer on top of a large flat diamond crystal substrate. The synthetic diamond forms the core component of what is called a Raman laser, a type of laser that is optically stimulated rather than electrically powered.

“Though there has been little take up of this type of diamond in the gem market, it is very well suited to our purposes. Diamonds larger than one centimetre are likely to be available very soon which will also be an advantage for our studies.”

Diamond is also the most transparent material known to man, in terms of the range of light wavelengths (or colours) that can pass through the material. Mildren said this would enable researchers to select from a huge range of laser wavelengths, such as in the far infrared, and hence potentially tap into a broad range of applications.

“The wide wavelength or colour choice means that we can tackle key challenges facing society in several areas. I'm aiming to attract junior researchers to start investigating devices that might solve key challenges in neurosurgery, or to safely detect toxic or explosive gases from a distance, a challenge that is considered a major priority for defence and counter terrorism organisations,” Mildren said.

Mildren said satellite borne diamond lasers for mapping greenhouse gases in the atmosphere were also a possibility. He said it is only now – in the 50th year since the invention of the first laser – that the full potential of diamond lasers is starting to be understood.

“It's a nice surprise to get a new type of laser to explore in the laser's big jubilee year,” Mildren said. “Two things came together only recently. Particularly good quality synthetic diamond is now being grown in Europe; and our knowledge of laser design is improving, thanks to work being done here at Macquarie and by several groups overseas using other materials that behave in a similar way.”

Mildren will present his work at the international conferences, Conference on Lasers and Electro-Optics and the Quantum Electronics and Laser Science Conference, being held together in California in May.

via Newsroom – Macquarie University.

But there is, of course, a catch. Although magnesium is abundant, its production is neither cheap nor clean, says Takashi Yabe of the Tokyo Institute of Technology. Various industrial methods are used to extract magnesium, ranging from an electrolytic process to a high temperature method called the Pidgeon process, but the energy cost is high. Producing a single kilogram of magnesium requires 10kg of coal, says Dr Yabe.

To change this, he is developing a process using only renewable energy. Dr Yabe’s solution is to use concentrated solar energy to power a laser, which is used to heat and ultimately burn magnesium oxide extracted from seawater—where, he says, there is enough magnesium to meet the world’s energy needs for the next 300,000 years. A solar-pumped laser is necessary, he says, because concentrated solar energy alone would not be enough to generate the 3,700˚C temperatures required. Dr Yabe calls his approach the Magnesium Injection Cycle.

The pure magnesium can then be used as a fuel (its energy density is about ten times that of hydrogen). When the magnesium is mixed with water, it produces heat, boiling the water to produce steam, which can then drive a turbine and do useful work. The reaction also produces hydrogen, which can be burned to produce even more energy. The byproducts are water and magnesium oxide, which can then be converted back into magnesium using the solar laser.

The trouble is that concentrated solar collectors tend to be huge and costly, and solar-pumped lasers are normally very low powered. Dr Yabe’s trick is to use relatively small Fresnel lenses—transparent and relatively thin planar lenses made up of concentric rings of prisms. These are commonly found in lighthouses to magnify light in a way that would normally require a much larger, thicker lens. His other trick is to boost the output power of the lasing material, neodymium-doped yttrium aluminium garnet. It normally only absorbs about 7% of the energy from sunlight, but when doped with chromium this figure increases to more than 67%.

Dr Yabe has built a demonstration plant at Chitose, Japan, in partnership with Mitsubishi. It is capable of producing 80 watts of power from the laser, enough to cut steel and extract 70% of the magnesium in seawater. The process will, says Dr Yabe, become commercially viable when the laser power reaches 400 watts, which could happen later this year. “As a starting point we are planning to use 300 lasers to produce 50 tonnes of magnesium per year,” he says. After that, it is just a small matter of convincing the world to start thinking about a magnesium economy instead of hydrogen one, he adds.

via Magnesium power: White-hot energy | The Economist.

Researchers have found a way to naturally double the frequency of laser light with an optical microresonator made from lithium niobate that supports “whispering gallery” modes.

Naturally Phase-Matched Second-Harmonic Generation in a Whispering-Gallery-Mode Resonator

J. U. Fürst, D. V. Strekalov, D. Elser, M. Lassen, U. L. Andersen, C. Marquardt, and G. Leuchs

Phys. Rev. Lett. 104, 153901 (2010) – Published April 12, 2010

via Physics.

The world's largest laser is meant to spark off a fusion reaction this year – but don't bank on it. So says the US government's watchdog in a critical report about the huge laser array at the National Ignition Facility (NIF).

Despite crucial success in evenly compressing fusion fuel pelletsMovie Camera earlier this year, the Lawrence Livermore National Laboratory's $3.5 billion array in Livermore, California, faces problems in repeating that success at the higher power needed for fusion, says a US Government Accountability Office (GAO) report.

via  New Scientist.

Physicists from Innsbruck study single-atom lasers

Rainer Blatt‘s and Piet Schmidt’s research team from the University of Innsbruck have successfully realized a single-atom laser, which shows the properties of a classical laser as well as quantum mechanical properties of the atom-photon interaction. The scientists have published their findings in the journal Nature Physics.

The first laser was developed 50 years ago. Today we cannot imagine life without the artificially produced light waves – lasers have become an integral part of many appliances used in telecommunication, household, medicine, and research. A laser normally consists of a gain medium, which is electrically or optically pumped, inside a highly reflective optical cavity (or resonator). The light in the cavity bounces back and forth in the form of modes whereby it is amplified repeatedly. One of the distinctive features of a classical laser is the steep increase of output power when a certain pumping threshold is reached. At this point the gain (amplification by the medium) equals the losses as the light circulates through the cavity. This is caused by the amplification of the interaction between light and atoms: The more photons are present in a mode the stronger the amplification of the light in the mode. This stimulated emission is usually observed in macroscopic lasers comprising of many atoms and photons.

The Innsbruck researchers have demonstrated that a laser threshold can be achieved at the smallest possible building block of a laser: a single atom, which interacts with a single mode in an optical cavity. A single calcium ion is confined in an ion trap and excited by external lasers. A high-finesse optical cavity consists of two mirrors, which traps and accumulates the photons emitted by the ion into a mode. The ion is excited cyclically by an external laser and at each cycle a photon is added to the cavity mode, which amplifies the light.

For strong atom-cavity coupling the regime of atom and cavity shows quantum mechanical behavior: Only single photons can be introduced into the cavity. “As a consequence, stimulated emission and threshold are absent,“ explains François Dubin, a French postdoc and first author of the publication. A ‘quantum laser’ was demonstrated in a similar regime some years ago. What is new in the experiment of the Innsbruck researchers is the ability to tune the coupling of the atom to the cavity mode. By choosing the right parameter of the drive laser, the physicists were able to achieve stronger excitation and, consequently, add more photons to the cavity. Although there was still less than one photon in the cavity, the researchers observed stimulated emission in the form of a threshold. “A single atom is a very weak amplifier. As a consequence, the threshold is much less pronounced than in classical lasers,“ explains Piet Schmidt.

An even stronger excitation does not result in a higher output, which is the case in a conventional laser, but in the quenching of the output due to quantum mechanical interference. This constitutes an intrinsic limitation of miniature single-atom lasers. Therefore, researchers from the University of Innsbruck want to further investigate the transition between quantum and classical lasers through the controlled addition of more and more ions interacting with the light field.

This research work is supported by the Austrian Science Fund, the European Commission and the Federation of Austrian Industry Tirol.

Publication: F. Dubin, C. Russo, H.G. Barros, A. Stute, C. Becher, P.O. Schmidt and R. Blatt, „Quantum to classical transition in a single ion laser“, Nature Physics, published online: 28 March 2010 | doi: 10.1038/NPHYS1627. (http://dx.doi.org/10.1038/NPHYS1627)

via 28.03.: From a classical laser to a “quantum laser“.