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Quanta 3

Frontiers 4Strange mass pinned down ●A visible quantum effect ●3D object optically cloaked●Controlling light on the nano-scale ●Pure water for disaster victims

News & Analysis 7LHC physics programme begins ●Report warns of NIF ignition delays ●Underwatersolution for storing wind energy ●China boosts nuclear power ●Obama outlinesNASA vision ●Europe launches ice mission ●UK announces first space agency●Mystery over Iranian physicist ●US unveils nuclear-weapons plan ●Science in theUK general election ●A laser to break the vacuum

Feedback 14Itsy-bitsy units and comments from physicsworld.com

The laser at 50From ray-gun to Blu-ray 16Sidney Perkowitz reveals how lasers in fiction have kept up with lasers in fact – or is itthe other way round?

And then there was light 23The laser’s early years were full of scientific creativity, public-relations spin andintense rivalry, as Pauline Rigby describes

Fusion’s bright new dawn 28Mike Dunne explains how a much anticipated breakthrough in laser fusion couldtransform the search for abundant, carbon-free electricity

Timeline: light fantastic 34Highlighting a few of the applications, awards and “firsts” in the laser’s rich history

The bubble legacy 36The telecoms crash of the early 2000s may have been a turbulent time for investors,but several key laser-based technologies from that period have been hugelysuccessful. Jeff Hecht reports

Going for green 43Mobile-phone companies want scientists to devise green laser diodes with powers ofat least 50 mW. Andy Extance explains why, and reveals the competing physicalphenomena – and companies – involved in this race

Beyond ultrafast 47Adrian Cavalieri tells us how to create laser pulses as short as 80 attoseconds, andhighlights some of the ultrafast physical processes these pulses can reveal

Where next for the laser? 53Six experts review the past and predict the future of lasers in different areas of physics

Careers 58Supporting laser science Harald Ellmann ●Once a physicist: Fausto Morales

Recruitment 62

Lateral Thoughts 68A villain’s life in lasers Kate Oliver

Shine on – the laser in everyday life 16–20

Physics World is published monthly as 12 issues per annualvolume by IOP Publishing Ltd, Dirac House, Temple Back, Bristol BS1 6BE, UK

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On the coverThe laser at 50 (Kate Gardner, Louise Mayorand Dens Milne) 15–56

Fast forward – attosecond light pulses 47–51

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physicsworld.com Contents: May 2010

1Physics World May 2010

http://www.cambridgetechnology.comhttp://www.cambridgetechnology.com

The possibility for discovery is off the chart

Nobel laureate Sam Ting quoted in the ObserverTing’s $300m Alpha Magnetic Spectrometer,which will attempt to discover the origin of high-energy cosmic rays, will finally get a trip to theInternational Space Station towards the end of theyear on one of the final Space Shuttle launches.

It is very difficult; it is really difficult

NASA boss Charles Bolden talking to the BBCBolden was close to tears during an interview whenasked to reflect on his time as an astronaut and todescribe what it means to him to witness the endof the shuttle programme, which has run for morethan 30 years.

It is extraordinary that this action hascost £200 000 to establish themeaning of a few wordsScience writer and physicist Simon Singh quotedin the GuardianSingh penned a comment piece for the Guardian inApril 2008 criticizing the British ChiropracticAssociation (BCA) for claiming its members coulduse spinal manipulation to treat children with earinfections, asthma and other ailments. The BCAthen sued him for libel denying these criticisms.Last month Singh won the right to use “faircomment” in his defence.

It is a very low bar – there is basicallyme and Patrick MooreParticle physicist and broadcaster Brian Coxquoted in the Daily MailCox, who came 70th in People magazine’s 100 sexiest men of the year, comes over allmodest when praised for being “good-looking…fora scientist”.

I have never forgiven them – myGerman is still pitifulQueen guitarist Brian May quoted in EurekaMay, who finally completed his PhD inastrophysics in 2007, still regrets being forced tostudy German at school on the grounds that itwould help him to understand physics papers byGerman researchers.

They have been a breath of fresh air

Environmentalist James Lovelock quoted in The TimesLovelock says that climate sceptics have kepteveryone from regarding the science of climatechange as a religion.

For the record

Quanta

The jokes are on CERNWith the Large Hadron Collider (LHC)having just recorded it first high-energy collisions, the CERN particle-physics labnear Geneva was, perhaps not surprisingly,the main focus of last month’s physics-based April fool gags. The Independent,rather lamely, claimed that a successor tothe LHC – dubbed LHC II – was earmarkedto go in the 23 km circumference Circle lineof the London Underground. Meanwhile,technology website CNET UK announcedthat a man had been arrested at the LHCafter having travelled back in time to tryand prevent the collider from starting upand destroying the world. Keen not to missout, a CERN press release noted the LHChad made its first discovery since it collided protons at 3.5 TeV per beam on 30 March.The release claimed that two researchershad found a paleoparticle, nicknamed“neutrinosaurus” because of its“prehistoric origins”. Yawn. Possibly thebest April fool was by physicist Adam Falkowski from Rutgers University,who announced on his blog Resonaancesthat the “unmistakable” tracks of asupersymmetric particle had been found by the ATLAS detector at CERN. At leastone Nature reporter fell for the gag anddouble-checked with CERN if thediscovery was true. Now that is funny.

Physics à la carteThe culinary limit of most universityphysics students is probably beans on toast,with, if they are feeling especially creative,a splash of chilli sauce on top. But studentsat Harvard University might be rustling upsomething much more exciting in thefuture. This autumn the renowned chefFerran Adrià, from the world famous,three-Michelin-starred restaurant El Bulliin northern Spain, will begin teaching culinary physics at the university. Over a13-week term, Adrià will team up withfellow Spanish chef José Andrés to helpstudents get to grips with the requiredparameters to make a decent dish.

Students on the course can look forward todemonstrations from the chefs on, forexample, how to make bubbles of airsurrounded by a thin sheet of fluid, whichare the inspiration for Adrià’s specialityfoams of beetroot, mushroom andexpresso. Whether Harvard students willnow be rustling up Adrià’s signature dishes– intertwined carrot chips with lemonverbena, ginger and liquorice followed bymelon caviar – remains to be seen.

Lambs for the chopIf you read the Sun, then you might be forgiven for thinking that the laser is not ahuman invention. According to a report inthe paper last month, some UK farmersnear Shrewsbury believe that advancedalien civilizations have been using lasers toattack their sheep. Former steelworker Phil Hoyle, who has spent a decade investigating unexplained livestock deathsin the area, says the attacks are beingcarried out by two orange-coloured spheresthat zap the sheep and remove their brainsand eyes. “The animals are being clinicallyand surgically sampled by a highlyadvanced technology,” an alarmed Hoyletold the newspaper. Having interviewedfarmers, he notes that “all but one” hadexperienced the disappearance or strangedeath of one of their animals. Hoyle offersno explanation for the aliens’ prowess withlasers but says that the devices must be built“by technology and intelligence that’s notfrom here”. The mystery continues.

Buzz offHe may have been thesecond man to step on theMoon, but Buzz Aldrinprobably spent more timeon the lunar surface thanhe did on the US TV showDancing with the Stars.

The 80-year-old former astronaut becamethe second celebrity to be voted off theshow last month and recorded the week’slowest score from the judging panel.Despite training for five hours a day beforehis stage debut, Aldrin gained only 13 points out of 30 for his waltz, which he performed with dance partner Ashly Costa.However, Aldrin’s appearance had an ulterior motive – to promote the US spaceprogramme and its future direction. “[I did] the best I could to spread interestamong Americans and the rest of the world about the achievements of successthat I was a part of in the past,” he toldEntertainment Weekly.

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3Physics World May 2010

A collaboration of particle physicists inEurope and North America has calculatedthe mass of strange quarks to an accuracy ofbetter than 2% – beating previous results bya factor of 10. This is the first time that themass of one of the lighter quarks has beenconstrained to such accuracy and could helpexperimentalists to scrutinize the StandardModel of particle physics.

It is notoriously difficult to determine themass of quarks because these elementaryparticles never exist in isolation – instead thestrong force constrains them into boundstates called hadrons, such as the proton andthe neutron. The picture is complicated be -cause a large portion of the hadron mass isbelieved to belong to the strong force itself,mediated by particles known as gluons, andthe exact nature of gluon–quark interactionsis poorly understood. Theorists thereforehave to combine measurements of hadron

behaviour with calculations based on quan-tum chromodynamics (QCD), the theory ofthe strong force, to define the mass of singlequarks. Refinements to this theory over theyears have enabled physicists to calculate themass of the heavier three quarks – the top,bottom and charm – to an accuracy of 99%.Unfortunately, it is has been much more dif-ficult to make accurate predictions for themass of the three lighter quarks – the up,down and strange – so reference tables stillcontain errors of up to 30%.

Christine Davies at the University of Glas -gow and colleagues in the High PrecisionQCD Collaboration have, however, taken a different approach, known as “latticeQCD”. The technique, which requires theuse of supercomputers, enables theorists toconfine the highly nonlinear strong interac-tion by defining quarks as nodes on a gridand gluons as the connecting lines. Davies’team adapts lattice QCD to calculate a ratioof the mass of the charm quark to the massof the strange quark. As the charm mass iswell known, the researchers can estimate thestrange quark mass to be 92.4 ± 2.5 MeV/c2(arXiv:0910.3102v2).

The result will be of particular interest toresearchers at CERN’s LHCb experiment,who, by studying mesons made of bottomquarks, are trying to recreate conditions fromshortly after the Big Bang. “This is all part ofpinning down the Stan dard Model and ask-ing how nature can tell the difference be -tween matter and antimatter,” says Davies.

Physicists in the US have observed quantumbehaviour in a macroscopic object largeenough to be seen with the naked eye – a thindisc-shaped mechanical resonator measuringabout 6.25 mm × 6.25 mm and consisting ofaround a trillion atoms. In making their ob -servations, Andrew Cleland and colleaguesat the University of California, Santa Barbara(UCSB) have exploited one of the funda-mental principles of quantum mechanics –objects being in two states at the same time.

To achieve these “superposition states”,an object needs to be cooled down to itsquantum ground state, at which point theamplitude of its vibrations is reduced to closeto zero. Until now, such states have onlybeen induced in objects up to the atomicscale and some larger molecules, such as“buckyballs”, which are made up of 60 car-bon atoms. However, the temperature towhich an object needs to be cooled in order

to reach its ground state is proportional to itsfrequency. As the aluminium-based “quan-tum drum” used in the UCSB experimentresonates at about six billion vibrations persecond, it could reach this resonation stateat “just” 0.1 K. “A regular tuning fork, forexample, would need to be cooled by an -other factor of a million to reach the samestate,” says Cleland.

The team measured the quantum state ofthe resonator by connecting it electrically toa superconducting quantum bit, or “qubit”,that was used to excite a single phonon in theresonator. This excitation was then trans-ferred many times between the resonatorand qubit to enable the researchers to createa superposition state in the resonator wherean excitation and a lack of excitation existedsimultaneously. When the researchers meas -ured the state, via the qubit, the resonatorhad to “choose” which state it was in (Nature464 697). The experiment could enable re -searchers to study the boundaries betweenthe quantum and classical worlds.

Frontiers

Element 117 createdScientists in Russia and the US have created a newelement with 117 protons by firing calcium-48ions at a target of berkelium-249. Although nuclearphysicists had previously synthesized a total of 27 elements heavier than uranium, element 117had remained elusive because the target materialneeded to produce it – berkelium-249 – is sodifficult to make. The researchers managed,however, to produce 22 mg of it by intense neutronirradiation over two years, which they then firedcalcium-48 ions at over a 150 day period. The newelement is the most neutron-rich isotope yetproduced, but its half-life of 78 ms is 87 timeslonger than a previously discovered isotopecontaining one neutron less. This supports the ideathat neutron-rich superheavy nuclei could beextremely stable (Phys. Rev. Lett. at press).

Gravitational waves within sightFluctuations in the curvature of space–time knownas gravitational waves could be discovered within ayear of current detectors being upgraded, providedthat the detectors focus their search on emissionsfrom binary black holes. That is the view ofastrophysicists in Poland, who believe there aresignificantly more of these astrophysical systemsthan was previously thought. After analysing datafrom the Sloan Digital Survey, the researchersfound that 50% of stars in a sample of 300 000galaxies have a lower “metallicity” than the Sun,which makes them much more likely to form black-hole binaries as they lose less mass at theend of their lives. Upgrades to the LIGO and VIRGOexperiments, to be completed by 2015, should givethem the sensitivity to detect these gravitationalwaves “within the first year of operation”, claim theresearchers (arXiv:1004.0386).

Wonder material steals the lightResearchers at IBM have made the firstphotodetector from graphene – a sheet of carbonjust one atom thick. Photodetectors convert opticalsignals into electrical current and they are widelyused in communications and sensing. Theresearchers needed to overcome a rare flaw ingraphene: the electrons and holes in the bulk ofthe material recombine too quickly, which leavesno free electrons to carry current. They applied aninternal electric field via palladium or titaniumelectrodes that are on top of multilayered or single-layered graphene, which separates theelectrons and holes. The graphene photodetectorcan detect optical data at rates of 10 Gbit s–1; thiscompares well with optical networks made of othermaterials, such as group III–V semiconductors(Nature Photonics 10.1038/nphoton.2010.40).

Strange quark weighs in precisely

I spy quantum behaviour

In brief

Read these articles in full and sign up for freee-mail news alerts at physicsworld.com

Elementary stuff “Strange” quarks are the heaviest ofthe three light quarks.

Chris

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4Physics World May 2010

Each year, two million people – mostly children –die from water-borne diseases such as diarrhoeaand cholera, according to the United Nations.Particularly vulnerable are those affected bynatural disasters, when gaining access to cleanwater can be a problem. However, a new techniquethat produces drinking water from seawater usingjust small amounts of energy could help to addressthis dire situation.

The technique, developed by researchers at theMassachusetts Institute of Technology (MIT) in theUS and Pohang University of Science andTechnology in Korea, manages to desalinate waterusing a simple electronic system. The processstarts by passing water along a tiny, 500 μm widechannel on a polymer chip. When the waterreaches a junction, it splits off into two separatetubes. By applying an electric potential along oneof these tubes, salt ions are dragged towards thischannel in the form of brine, while desalinatedwater flows down the second channel under theforce of gravity. The researchers have successfullyused the technique, which is dubbed ionconcentration polarization (ICP), to convertseawater, with a salinity of 30 000 mg l–1, intofresh water with a salinity of less than 600 mg l–1,which meets the international standards for waterpurity (Nature Nanotech. 5 297).

In terms of energy consumption, ICP comparesfavourably with established methods ofdesalination, requiring less than 3.5 Wh l–1.Reverse osmosis, for example, which works byforcing seawater through a membrane at highpressures to capture the salt, requires 10–15 Wh l–1. And electrodialysis, which works bytransporting salt ions from one solution to anotherby means of ion-exchange membranes, requires5 Wh l–1. Another advantage of ICP is that it canremove other potentially harmful larger molecules– such as cells, viruses and bacteria – without thefilter becoming heavily clogged, a problem thataffects both reverse osmosis and electrodialysis.

The next challenge is to scale up the device intoa viable technology. As one chip produces just10 μl per minute, the researchers estimate thatthey will need 10 000 combined units to produce auseful amount of water in a realistic time. A devicethis size would still be portable at just 30 ×20 cm.Sung Jae Kim, one of the researchers at MIT, told Physics World that his team hope to haveproduced a 100-unit device within two years. One outstanding challenge is to ensure that alldangerous hydrocarbons and heavy metals arealso removed from the seawater, which is notguaranteed with the current device.

Tiny desalination devicecould help aid efforts

While this dented cuboid may not look particularly magical, it represents a key breakthrough in one of themore mind-bending areas of physics – the pursuit of invisibility. It is the first device that can hide an objectfrom near-visible light in three dimensions – albeit a very small bump with a height of just 30 μm. Thedesign is known as a “carpet cloak” because it involves smoothing out a bump on a surface as if flatteningout a ruck in a rug. The cloak was fabricated by Tolga Ergin and colleagues at the Karlsruhe Institute ofTechnology (KIT) in Germany, together with John Pendry of Imperial College London. The team built thecloak by stacking nanofabricated silicon wafers on top of one another in a “woodpile” matrix and thenfilling in the gaps between the wafers with varying amounts of polymer. This produces a distribution ofrefractive indices within the structure that can achieve an optical transformation whereby light appears toreflect off the device as if an object were not there. To demonstrate the technique, the researchers placedtheir device on top of a reflective gold surface containing a small bump with dimensions of30 μm×10 μm×1 μm. This set-up produced a cloaking effect using unpolarized infrared light withwavelengths between 1.4 μm and 2.7 μm (Science 10.1126/science.1186351). Importantly, this effectheld for viewing angles of up to 60° (with 0° representing viewing in just two dimensions). Last year thissame cloaking technique was used to hide objects at micro and infrared wavelengths, but these cloakswere limited to two dimensions. Team member Martin Wegener from KIT says that it should be possiblewith existing technology to make the cloak bigger in order to hide even larger objects, but that thisapproach would be extremely time-consuming. “Faster nanofabrication tools will have to be developedthat allow for 3D structures,” he says.

Innovation

Nanotechnology in science fiction usuallyinvolves familiar objects being cleverlyshrunk to the scale of individual molecules.In a rare example of that vision becoming a reality, researchers in Japan have built anano-scale version of a classic TV antennabut in this case it can transmit light.

The “Yagi–Uda” antenna was invented byJapanese scientists in 1926 to overcome sig-nal degradation, whereby radio signals de -grade when transmitted over long distances.It was used by the British with radar duringthe Second World War and went on to be -come the standard antenna for transmittingand receiving television signals. Key to theclassic design is its “parasitic elements”,made from strips of electrical conductors,which boost radio transmissions by produ -cing secondary signals in the same directionwhen a current is induced in the presence of

the original signal. The same principle worksin reverse, so the antenna can also boost a sig-nal when receiving information.

Yutaka Kadoya and colleagues at Hiro -shima University have now adapted theYagi– Uda design to control light at the nano-scale by replacing the conducting strips withan array of five gold nanorods. The nanorodsare aligned in such a way that incoming lightmanages to trigger plasmons in the gold sur-face – collective wavelike motions of billionsof electrons – to resonate and emit secondarylight in the same direction. The re searchersdemonstrated the technique for red light witha wavelength of 662 nm (Nature Photonics10.1038/nphoton.2010.34). They now want tointegrate their design with fluorescent mole-cules to create a coupled device that couldform the basis of a new sensing technique forthe medical sciences.

Antenna shrunk for the nanoworld

3D invisibility cloak unveiled

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physicsworld.com Frontiers

5Physics World May 2010

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The physics programme at CERN’sLarge Hadron Collider (LHC) is nowunder way and the Geneva lab says itis making good progress with increas-ing the number of proton–proton col -lisions. The first collisions at 7 TeV,marking the start of the LHC’s phys -ics programme, occurred on 30Marchand all four of the LHC’s experimentshave been collecting data since then.“A lot of people have waited a longtime for this moment, but their pa -tience and dedication are starting topay dividends,” said CERN director-general Rolf-Dieter Heuer.

Heuer’s delight at the LHC finallycolliding protons 18 months after itsstart-up, was shared by Fabiola Gia -notti, spokesperson for the ATLASex periment. “The prevailing senti-ment is emotion,” she said shortlyafter the first collisions were an -nounced. “Behind these instrumentsare people with their feelings, withtheir frustrations, with their ambitions– it is the end of 20 years’ hard workwithin the scientific community.”

Researchers at the lab are so farpleased with the quality of the collisiondata they have received. “By autumn,it is going to get quite interesting here– we will be frantically looking at thedata,” says Albert de Roeck, deputy

spokesperson for the Compact MuonSolenoid (CMS) ex periment. “We willhave our first pop at the Higgs at theend of the year – we will certainly ex -clude mass regions but discovery isgoing to be more difficult.”

The missing piece in the StandardModel of particle physics, the Higgsboson could explain how particlesacquire their mass. Precision meas-urements of known Standard Modelparticles mean that the mass of theHiggs is unlikely to be more than186 GeV, while direct searches madeat CERN’s Large Electron–Positroncollider (LEP) – the forerunner to theLHC – have ruled out a Higgs that is

lighter than 114 GeV.Some researchers, however, be lieve

that it could take much longer toprove decisively whether the Higgsdoes exist. “From previous findings at the Tevatron [at Fermilab in theUS] and theoretical studies, it seemsmost prob able that the Higgs mass is a tick above 115 GeV,” says HanspeterBeck, a researcher at the ATLAS ex -peri ment. “And, if it is there, it will beultra difficult [to find] and will take upto six years to prove or disprove if itex ists,” he adds.

Meanwhile, Niko Neufeld, a staffscientist at the LHCb experiment,which will study the difference be -tween matter and antimatter with un -precedented accuracy, is optimisticthat it can start producing “seriousphysics” within a few months. “To -wards the end of this year we shouldbe in full swing and hopefully have thefirst drafts of pa pers for the winterconferences of next year,” he says.

CERN plans to run the LHC con-tinuously for 18 to 24 months, with ashort technical stop at the end of 2010.The LHC will then shut down in 2012to prepare it to go to maximum-energy14 TeV collisions, probably in 2013.James DaceyGeneva

News & Analysis

LHC ramps up its search for the Higgs

Watchful eyesStaff in CERN’scontrol room await7 TeV collisions.

Hopes of reaching a milestone in fusionresearch by the end of 2010 have dimmedfollowing a US government report thatplays down the chances of an earlybreakthrough and sharply criticizesmanagement of the $4bn NationalIgnition Facility (NIF). In the report,officials from the GovernmentAccountability Office (GAO) state thatignition – fusion’s “break-even” point – is“unlikely” to occur at the laser-fusion labthis year and that “significant scientificand technical challenges” could delay oreven prevent the facility from achievingignition by 2012.

NIF’s plan for ignition relies on beingable to focus up to 1.8 MJ energy from192 laser beams onto a 2 mm-diameterberyllium sphere filled with deuteriumand tritium fuel. Radiation pressure from

the beams will then cause the sphere toimplode, fusing the deuterium andtritium nuclei and setting off a sustainedburn that produces excess energy (see pp28– 33).

Although a NIF spokesperson toldPhysics World that the lab “never claimedit would achieve fusion ignition in 2010”,expectations of an early breakthroughhad been raised in January, after NIFresearchers published results showingthat they could compress plastic testspheres smoothly at radiationtemperatures of up to 3.3 mK. Testsperformed shortly after the facilityopened in March 2009 had alreadydemonstrated that laser systems couldoperate at the high energies required.

But while the GAO acknowledges that“substantial progress” has been made, it

lashes out at the management of theproject. In particular, the report finds thata “weak oversight” by the NationalNuclear Security Administration (NNSA)has allowed NIF’s operator, the LawrenceLivermore National Laboratory, to delayconstruction of safety systems requiredfor ignition experiments. These includedconcrete doors needed to containradiation from neutrons produced in near-ignition reactions.

The NIF spokesperson says thatresearchers will initially performdiagnostic tests using ordinary hydrogen,rather than deuterium, to keep neutronlevels low. The proportion of deuteriumwill then be slowly increased, untilconditions are met for a full ignitionexperiment using 50% deuterium and50% tritium. The spokesperson adds thatthe “first credible attempts” at fusionwould still begin in 2010, emphasizingthat ignition is still expected within a yearor two.Margaret Harris

[We] neverclaimed itwould achievefusion ignitionin 2010

Fusion

Breakthrough at NIF ‘unlikely’ in 2010

CERN

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7Physics World May 2010

The future of wind energy could in -volve huge blades spanning half akilometre that generate compressedair – which is then piped into giant,underwater balloons. That is thedream of Seamus Garvey, a mechan -ical engineer at the University of Not -tingham in the UK, who envisagesusing the pressurized air to inflate the balloons, nestling about 500 mbelow the surface of the sea. Elec tri -city could then be generated, when re -quired, by releasing the air to drive aset of turbines.

The advantage of Garvey’s tech-nique is that several days’ worth ofenergy could be stored in the balloonswhile the wind is blowing – and thenreleased when there is no wind. Gar -vey has just formed a spin-out com-pany called NIMROD Energy tocommercialize the technology, dub -bed Integrated Compressed Air Re -newable Energy Systems (ICARES),which he has been working on since2006. He has also received a 7310 000development grant from the energycompany E.ON.

According to Garvey’s blueprint,the wind turbine’s blades would behollow and contain an internal piston.When the blade is pointing down-wards, the piston is at the tip. As theblade slowly lifts skywards, the piston

falls through the cylinder, compres -sing air. However, the blades must notrotate too fast or else the pistons willget pinned to the ends of the blades.Given that a blade’s rotation speed isinversely proportional to its length,Garvey’s scheme would only be prac-tical for turbines bigger than about230 m in diameter, with 500 m beingthe ideal size.

As for the storage balloons, Garveysays they should ideally be 20 m indiameter and lie anchored 500 mbelow the surface of the sea. He hasal ready begun to test prototype “en -ergy bags” and believes that that acommercial undersea storage systemwill be available by May next year.

Although Garvey believes that it willtake about 15 years to get the giantturbines up and running, he says hissystem could be as cheap to build as agas-turbine generator and have zerofuel costs.

Compressed-air energy storage isnot a totally new idea. There are twofacilities – one in Germany and theother in the US – where surplusenergy is taken off the electrical gridand used to pump air undergroundinto disused salt mines. But Garveysays that underwater storage has twobenefits. It is not restricted to minelocations, plus the pressure in an un -dersea bag is constant, which lets tur-bines generate electricity relativelyefficiently. An underground storagefacility, in contrast, has a fixed vol-ume, meaning that the air pressuredrops as air is released.

Garvey also thinks undersea bagscould store surplus energy from nuc -lear reactors or even natural gas.Jakob Mann, a wind-energy expert atRisø National Laboratory in Den -mark, says that the storage techniqueis “worthwhile trying” but warns thatthe undersea nature of the schemecould boost the cost. “Offshore is al -ways expensive,” he says.Hamish Johnston● See also page 14

Spin-out puts new spin on wind-energy technology

China has announced plans to generatean extra 100 GW of power from nuclearreactors – a 12-fold increase in nuclearcapacity. The plans, released in lateMarch by the Energy Bureau of theChinese National Development andReform Commission (NDRC), will see anadditional 75–80 GW of nuclear powercoming online by 2020, with a further25 GW of capacity still under constructionat that time. If the country completes itsplan, then nuclear power will account for about 5% of China’s electricity needsby 2020.

Last year, nuclear power capacity inChina was 9.08 GW, accounting for only1.04% of the total power generation inthe country, according to the ChinaElectricity Council, which implementsgovernment energy policy. Original plansby the NDRC, published in October 2007,announced that China would increase its

nuclear power capacity by 40 GW by2020 with a further 18 GW inconstruction. The revised plans almostdouble those figures.

“We will be building as many as six toeight 1 GW nuclear power plants eachyear,” says Mu Zhanying, general managerof Chinese National Nuclear EngineeringGroup Company. Chinese authorities have

identified 30 possible sites that canaccommodate nuclear power stations.

China is already building the world’slargest single nuclear power plant inTaishan City, on the southern coast of thecountry, close to Hong Kong. The 1.75 GWTaishan nuclear plant, costing $4.7bn, isthe first of two European PressurizedReactors to be built at Taishan and isexpected to come online in 2013, with thesecond following in 2014. Indeed, Sun Youqi, general manager of ChineseNational Nuclear Engineering GroupCompany, says that China is alreadybuilding more nuclear power capacitythan any other country in the world.

However, some worry about China’sability to deal with nuclear-fuelreprocessing and high-level radioactivewaste once the reactors are operating.“We need to pay far more attention nowto researching techniques into fuel post- processing”, says Li Yongjiang, theformer manager of the Qinshan NuclearPower Company.Jiao LiBeijing

Innovation

China plans massive nuclear boostEnergy

Bags of energySeamus Garvey fromthe University ofNottingham hasdesigned a way ofstoring wind energy inunderwater balloons.

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Power to the peopleOne of two 1.75 GWEuropean PressurizedReactors that China isbuilding in TaishanCity, near Hong Kong.

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physicsworld.comNews & Analysis

8Physics World May 2010

US President Barack Obama has an -nounced a new direction for NASAthat includes plans to send astronautsto an asteroid by 2025. Speaking lastmonth at Florida’s Kennedy SpaceCenter, the launching location for US manned spaceflights, Obama also called for a new “heavy-lift” rocketdesign to take astronauts on a missionto orbit Mars by the mid-2030s thatwill “eventually” be used to transporthumans to the Martian surface.

In February, the Obama admin -istration said it was cancelling theConstellation programme – first pro-posed by George W Bush in 2004 – to develop new “Ares” rockets thatwould allow astronauts to return tothe Moon by 2020. Critics argued thatthe decision would surrender USlead ership in space and extinguishthe country’s vision of exploration.Neil Arm strong, the first man to walkon the Moon, called the decision“devastating” and a waste of the$10bn in vestment in Con stellationand the years of re search and devel-opment put into the project.

The new plan involves retainingsome of Constellation’s technology,and NASA will now start to adapt its Orion crew capsule, which wouldhave hitched a ride on Ares to the

International Space Station (ISS), as a kind of “space lifeboat” to re ducere liance on foreign vehicles for rescuemissions to the ISS.

Obama also announced that NASAwill now invest more than $3bn in re -search on its heavy-lift rocket, with adesign expected to be complete “nolater” than 2015. The rocket, whichshould be complete a few years later,could be used for a trip to a near-Earth asteroid and then in a separatemission to Mars.

Obama noted that he expects to still“be around” by the time US astro-nauts land on the red planet. “We will

ac tually reach space faster and moreoften under this new plan, in ways thatwill help us improve our technologicalcapacity and lower our costs,” he said. “Nobody is more committed tohuman exploration of space than I am.But we’ve got to do it in a smart way.”

The new plans also include mod-ernizing the Kennedy Space Center,as well as upgrading its launch capa-bilities. That process should createmore than 2500 extra jobs in the re -gion, compensating in part for joblosses that will occur due to the plan -ned end of the Space Shuttle pro-gramme this year. Obama called aswell for NASA and other governmentagencies to develop a plan by 15 Au -gust for economic growth and job cre-ation in the region.

In his speech, Obama also ex -plained where an additional $6bnover the next five years for NASA willbe spent. First announced in his 2011budget request to Congress, this newmoney will go on increasing Earth-based observations, extending the lifeof the ISS by more than five years to2020, as well as working with privatecompanies to make getting to spaceeasier and more affordable.Peter GwynneBoston, MA

Obama sets out NASA’s new mission to Mars

A satellite that will probe how muchthe Antarctic and Greenland icesheets are contributing to global sea-level rises was successfully launchedfrom the Baikonur Cosmodrome inKazakhstan last month. The 7135mCryoSat-2 satellite, built by the Eu ro -pean Space Agency (ESA), will alsomeasure tiny variations in the thick-ness of ice floating in the polar oceans.Weighing 700 kg, CryoSat-2 is noworbiting the Earth around its poles720 km above sea level.

CryoSat-2’s main instrument is theSynthetic Aperture InterferometricRadar Altimeter (SIRAL), which isdesigned to send a burst of microwavepulses towards the Earth every 50 µs.The returning echoes can then beused to measure the distance betweenthe satellite and the sea ice, fromwhich a 3D map of the thickness offloating sea ice lying above sea levelcan be built to an accuracy of a few

centimetres. Researchers can thenuse this information to estimate thetotal mass and thickness of ice flow,the bulk of which (some 90%) liesunder the water.

Set to remain in orbit for the nextthree years, CryoSat-2 will use thesame technique to measure changes tothe thicknesses of huge land-ice sheets,

such as those in the Antarctic andGreenland. CryoSat-2 is the satellite’ssecond incarnation after CryoSat-1was destroyed by a launch failure fiveyears ago. In 2006 ESA decided torebuild the satellite and launch it in2009, but delays led to the take-offbeing postponed until last month.

“We are very much looking forwardto delivering the data the scientificcommunity so badly needs to build atrue picture of what is happening inthe fragile polar regions,” says physi-cist Richard Francis, project managerof CryoSat-2. CryoSat-2 is the third ofseven Earth-monitoring satellites thatform the ESA’s Earth Explorer pro-gramme. The first – the Gravity Fieldand Steady-state Ocean CirculationExplorer (GOCE) – was launched inMarch 2009, while the Soil Moistureand Ocean Salinity (SMOS) space-craft took off last November.Michael Banks

Space

Europe’s ice mission successfully blasts off

One giant leapNASA plans to sendastronauts on amission to orbit Marsby the mid-2030s,with a landing sometime after.

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Second time luckyThe European SpaceAgency’s CryoSat-2satellite will monitorice thicknesses.

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physicsworld.com News & Analysis

9Physics World May 2010

A new body that will be responsiblefor the UK’s space policy and bring all key budgets for space under a single management was establishedlast month. The UK Space Agency(UKSA) will manage about £250m incontracts each year, including theUK’s contribution to major Europeanprojects such as the 73.4bn Galileoglobal positioning system and theGlobal Mon itoring for Environmentand Security initiative. Both projectsare currently supported by the UK’sdepartment for transport, and the de -partment for environment, food andrural affairs, respectively.

The UKSA, which will have itshead quarters in Swindon, will be ledby David Williams, director generalof the British National Space Centre,until a permanent chief executive isappointed within the next six months.“The action we are taking shows thatwe’re really serious about space,”said science minister Lord Draysonat the agency’s launch last month. Heclaimed that the agency will help the UK’s space industry to grow from£6.5bn to £40bn a year and create

100 000 jobs within the sector overthe next 20 years.

The UK currently spends about£300m per year on civil space re search,a large fraction of which – some £240m in 2009 – goes on the country’smembership of the Euro pean SpaceAgency (ESA). The rest of the cash isspent on its membership of the Eu ro -pean Organisation for the Exploi -tation of Meteorological Satel lites,which launches and maintains Earth-observation satellites and is currentlyfunded by the UK’s Met Office.

At the UKSA launch, Drayson andbusiness secretary Lord Mandelsonalso announced a £40m InternationalSpace Innovation Centre (ISIC) to bebased at Harwell in Oxfordshire nextto the European Space Agency’s tech-nical facility, which opened last July.Designed to bring together industryand academia, ISIC will seek to ex -ploit data from Earth-observationsatellites, use space data to under-stand climate change, and advise onthe “security and resilience of spacesystems and services”.Michael Banks

UK launches space agency to manage all contractsSpace science

Climate inquiry clears researchers“We saw no evidence of any deliberatescientific malpractice in any of the work ofthe Climatic Research Unit and had it beenthere we believe that it is likely that wewould have detected it.” That is the mainconclusion of an independent panel ofscientists, nominated by the UK’s Royal Society, to scrutinize the scientificmethodology of researchers at the ClimateResearch Unit (CRU) at the University ofEast Anglia. The seven-member panel wasset up by the university and chaired by Lord Oxburgh – a geologist and former oil-company executive. The report, whichlooked at 11 “representative publications”from CRU members over the past 24 years,was commissioned after private CRU e-mails were hacked last year and madepublic. Critics alleged that the e-mailsshowed that the scientists incorrectlyinterpreted data to support man-madeclimate change and flouted freedom-of-information requests to make data andcomputer code available.

Egypt tops African physics outputEgypt, Nigeria and South Africa dominatescientific output in Africa, according to anew study from Thomson Reuters. It foundthat researchers in Egypt were the mostprolific in the north of the continent,accounting for 30 000 papers between1999 and 2008 – three times more thanfrom scientists in Tunisia. Nigeria was thedominant nation in central Africa,generating 10 000 papers in the sameperiod, while scientists in South Africa ledthe way in the south of the continent,publishing 47 000 papers in the decade to2008. Egypt is Africa’s top nation forphysics – producing 1880 papers between2004 and 2008. South Africa was secondwith 1194 papers and Algeria third with933 published articles.

Diamond wins £110m upgradeThe Diamond synchrotron light source inthe UK has received £110m of funding thatwill allow it to complete 10 morebeamlines. The planned upgrade, whichshould be completed by 2017, will bringthe total number of beamlines at thefacility to 32. The bulk of the money(£97.4m) comes from the Large FacilitiesCapital Fund (LFCF), which supportsinvestments made by Research CouncilsUK – the umbrella organization for theseven UK funding councils. The remaining£13.8m comes from the Wellcome Trust –a UK-based biomedical charity. Diamondcurrently has 17 operational beamlines,which in two years’ time will be extended to 22.

Sidebands

On the upThe UK Space Agencywill manage about£250m in contractseach year.

An Iranian physicist who disappeared lastJune during a pilgrimage to Mecca inSaudi Arabia has apparently defected tothe US, where he is working for theCentral Intelligence Agency (CIA).Shahram Amiri, who did research innuclear physics at Malek AshtarUniversity of Technology in Tehran, isthought to be co-operating with the CIA toconfirm their intelligence assessmentsabout Iran’s nuclear-weaponsprogramme. The CIA has so far kept quieton the issue and it remains unclearwhether Amiri had any connections withIran’s nuclear programme.

According to various reports, Amiri wasinvolved in producing radioactive isotopesfor medical applications at Malek AshtarUniversity of Technology. The universitylies across the street from FEDAT – aninstitution run by the country’s Ministry ofDefence that carries out research anddevelopment on nuclear weapons.According to the Washington-basedorganization Iran Watch, in 2005 officialsin Germany linked the university to workon proliferation-sensitive nuclearactivities and the development of rockets

for nuclear weapons.Reza Mansouri, a physicist at Iran’s

Sharif University of Technology, toldPhysics World that he had never heard ofAmiri’s name before it came to light in themedia. “So you can imagine how he stoodin the physics community in Iran,” hesays. According to Steven Miller, aspecialist on Iran at Harvard University’sKennedy School of Government, itappears most likely that Amiridisappeared voluntarily.

Amiri is not the first individual withsuspected connections to Iran’s nuclearprogramme to disappear and reappear inthe West. Possibly the best known is Ali Reza Ashghari, a former deputydefence minister, who disappeared froma hotel in Istanbul three years ago andreportedly provided intelligence to theCIA. But Amiri’s loss is unlikely to affectthe Iranian nuclear programme. “Onceyou have acquired the knowledge ofuranium enrichment,” says Miller’scolleague Jason Blackstock, “it is almostimpossible to remove it.”Peter GwynneBoston, MA

Middle East

Iranian physicist ‘defects’ to the USOnce you haveacquired theknowledge ofuraniumenrichment, it is almostimpossible toremove it

physicsworld.comNews & Analysis

10Physics World May 2010

US President Barack Obama has sig-nalled a new approach to nuclear-weapons policy that limits their useagainst other states and documentshow the country will ensure the viab -ility of existing stockpiles. The Nuc -lear Posture Review (NPR), whichsets out the US’s nuclear strategyover a 10-year period, also calls for ahighly skilled workforce to ensure“the long-term safety, security andeffectiveness of the nuclear arsenaland to support the full range of nuc -lear-security work”.

The last NPR was conducted in2001 during the George W Bush ad -ministration, which kept its findingsclassified. The latest review, releasedlast month and made fully public, con-cludes that the US will not use nuclearweapons against non-nuclear statesthat are “in compliance” with theNuc lear Non-proliferation Treaty,even if they attack the US with bio-logical or chemical weapons. How -ever, the review makes it clear thatNorth Korea and Iran do not fall intothat category.

Carried out by the US Departmentof Defense and the Department ofEnergy, the review notes the need for

highly trained scientists and engin -eers to “sustain a safe, secure andeffective US nuclear stockpile as longas nuclear weapons exist”. It also says that existing nuclear weapons’lifetimes could be increased, rulingout the need for manufacturing new“reliable” replacement warheads.This had been recommended late lastyear by the JASON advisory group – a collection of independent scientistswho advise the US government onscience issues.

Some disagree with Obama’s decis -ion not to update the US’s nuclearweapons. “I think the administration

has made a mistake by not supportingthe [production of] reliable replace-ment warheads,” says Jay Davis,found ing director of the DefenseThreat Reduction Agency and a for-mer Lawrence Livermore NationalLaboratory scientist who is now presi -dent of the Hertz Foundation.

Immediately following the review,Obama and Russian President DmitryMedvedev signed up to the START-IITreaty, which will dramatically reducethe number of deployed nuclear weapons that each country has from1762 to 1550 for the US and 1741 to1550 for Russia. Although the Senatemust ratify the treaty by a two-thirdsmajority before it can come into force,it was welcomed by JASON memberSidney Drell, a senior fellow at Stan -ford Uni versity’s Hoover Insti tutionand former deputy director of theSLAC National Accelerator La bor at -ory. “Re ducing the reliance on nuclearweapons and reaffirming the commit-ment to go to zero is a strong and goodbasis,” he says. “And the commitmentto continued support for a science andtechnology base is important.”Peter GwynneBoston, MA

US changes course on nuclear-weapons strategyPolicy

Signing upUS President BarackObama and RussianPresident DmitryMedvedev havesigned a newagreement on nuclear weapons.

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ConservativesAdam AfriyieShadow minister forinnovation, universities and skillsBackground: After a BSc inagricultural economics fromImperial College London, in

1993 Afriyie became founding director of ConnectSupport Services – an IT services company. Afriyiewas elected as MP for Windsor in 2005. After servingin a range of committees on civil aviation and onscience and technology, he was made Conservativeparliamentary leader for technology, media andtelecoms in 2006 and then shadow minister forinnovation, universities and skills in 2007.Pearls of wisdom: “Our science base is a valuablenational asset. Economically, politically andsocially, it underpins the prosperity and wellbeingof our nation.”What the manifesto says: “Initiating a multi-yearscience and research budget to provide a stableinvestment climate for research councils.”Manifesto wordcounts: science/scientists (8);innovation (8); research (9); universities (14);physics (0)

LabourPaul DraysonMinister for science andinnovationBackground: Draysoncompleted a BSc inproduction engineering atAston University in 1982,

gaining a PhD in robotics in 1985. After becomingmanaging director of Lambourn Food Company in1986, he co-founded the Oxford-based vaccinecompany PowderJect Pharmaceuticals in 1993,where he was chairman and chief executive until2003. In October 2008 he was appointed as theminister of state for science and innovation, takingup a seat in the cabinet. In June 2009 he took onadditional responsibilities as defence minister.Pearls of wisdom: “Science isn’t peripheral to thedecision facing the country. It is central: to growth,to prosperity and wellbeing.”What the manifesto says: “We are committed to a ring-fenced science budget in the nextspending review.”Manifesto wordcounts: science/scientists (6);innovation (11); research (7); universities (17);physics (0)

Liberal DemocratsEvan HarrisLiberal Democratsspokesperson for scienceBackground: Evan Harris is aqualified doctor, havingcompleted his education atthe Oxford Medical School.

After working as a junior doctor at the Royal Liverpool University Hospital and the John Radcliffe Hospital in Oxford, Harris became anMP for Oxford West and Abingdon in 1997. In 2001he became shadow secretary of state for health,and since 2005 he has been the Liberal Democratspokesperson for science.Pearls of wisdom: “We recognize that science,technology and engineering have to be key driversof our economy as we move out of recession.”What the manifesto says: “In the current economicclimate it is not possible to commit to growth inspending, but the Liberal Democrats recognize theimportance of science investment to the recoveryand to the reshaping of the economy.”Manifesto wordcounts: science/scientists (12);innovation (5); research (9); universities (8);physics (0)

UK parties spell out science policies ahead of 6 May general election

physicsworld.com News & Analysis

11Physics World May 2010

This year is one of celebration for Gér -ard Mourou – and not just because2010 marks the 50th anniversary of theinvention of the laser. It is also 25 yearssince the 65-year-old French physicistpublished details of one of his mostcoveted contributions to laser science.Going by the rather ungainly name ofchirped-pulse amplification (CPA),the technique has enabled physiciststo create lasers that are orders of mag-nitudes more powerful than wereachievable without it (see box).

CPA now lies at the heart of mosthigh-powered laser facilities in theworld. It was used in the now-decom-missioned Nova PW system at theLawrence Livermore National La bor -atory in the US, which generatedrecord-breaking 1.3 PW (1.3 × 1015)pulses, and in the 1 PW Vulcan laserat the UK’s Rutherford Appleton La -boratory in the UK, which is in themidst of being upgraded to go beyondthe 10 PW level.

But now Mourou is designing alaser facility that will be so powerfulthat it can rip apart empty space itself.Mourou’s parting shot to the lasercommunity, the Extreme Light Infra -structure (ELI) will create very shortpulses of light barely 1 femtosecond(10–15 s) long with energies of severalkilojoules corresponding to petawattsof power. While other lasers such asVulcan can provide a high-poweredpulse every 20 minutes, ELI will beable to deliver one every few minutes.

Although ELI will be used for nuc -lear physics, attosecond physics andstudies of laser-based particle accel-eration, perhaps its most exciting pos-sibility is to test the properties of thevacuum, or empty space, itself. “Thisis not just a laser that is about break-ing the next re cord,” says Mou rou,who is ELI’s project coordinator anddirector of the Institut de la Lu mièreExtrême at the Ecole Na tion ale Su -périeure de Tech niques Avancées inFrance. “There is a fundamental rea-son be hind building it.”

Mourou first proposed ELI fiveyears ago and he has been the drivingforce behind the project ever since. In2006 it was chosen as one of 35 projectson a “wish list” of scientific facilitiesdrawn up by the European StrategyForum on Research Infra structuresthat researchers in Europe want to see

built within the next decade.The new laser facility quickly gar-

nered support with laser scientists inEurope, including Wolfgang Sander,director of the Max Born Institute fornonlinear optics and short-pulsespectroscopy in Berlin and the presi-dent-elect of the German PhysicalSociety. “ELI offers a factor of 100more in achievable power than any-where else in the world,” he says. “Alot of new physics could be done withit – it is revolutionary.”

A competition to build ELI wasbegun in 2007. Five countries – theCzech Republic, France, Hungary,Romania and the UK – initially bid tohost the project. But after the UK andFrance pulled out of the running, inOctober 2009 the ELI steering com-mittee decided to not build one singlefacility, but four – one in Romania onnuclear physics, another in Hungaryon attosecond physics, a third onlaser-based particle-beam productionin the Czech Republic and a fourth inultrahigh-powered lasers. The latter’slocation is still up for grabs.

The 7250m needed to build each ofthe first three of these facilities will bemet by the host nation and construc-tion is due to start at the end of theyear. Once up and running in 2015, anumber of European member statesbe longing to the European ResearchInfra struc ture Consortium are ex pec -ted to pay for labs’ operational costs.

Surfing electronsThe Czech facility, which will be builtin Prague, will seek to generate forthe first time pulses with a few peta -watts in power at a frequency of about100 Hz. These femtosecond laser pul -ses will be fired into a gas to create anelectron–proton plasma that could beused to make a very compact particle

Four for the futureThe Extreme LightInfrastructure willconsist of fourfacilities, includingthis one in the Czech Republic thatwill use short pulsesof light to testacceleratingelectrons with lasers.

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Breaking the vacuumEurope is planning to build the world’s most powerful laser that willliterally rip empty space apart. Michael Banks lifts the lid on the Extreme Light Infrastructure

All four sites belonging to the Extreme LightInfrastructure project have one aspect in common:a way of generating very short pulses of light at very high energies. At their heart, the four facilitieswill use the chirped-pulse amplification (CPA)technique invented 25 years ago by GérardMourou, now director of the Institut de la LumièreExtrême at the Ecole Nationale Supérieure deTechniques Avancées in France.

To generate the high-energy beams, a standardoff-the-shelf table-top laser source will be used togenerate pulses that are a femtosecond in length.These pulses, however, only have a small amountof energy – about a nanojoule. To get a high-powered petawatt beam, the energy needs to beincreased by a factor of about 1012. However, asthe energy of a short-pulse laser beam is

amplified, the refractive index of the medium it ispassing through starts to change; and once thepower of the beam goes beyond a few gigawatts, itstarts to produce nonlinear effects in the medium.This can lead to so-called self-focusing, where theintensity of the beam increases rapidly damagingthe optics in the process.

To keep the intensity of laser pulses below thethreshold of nonlinear effects, laser systems hadto be very large and expensive, and the peak powerof laser pulses was still limited to a few terawattsfor very large multibeam facilities. In 1985Mourou, then at Rochester University, US, and his colleague Donna Strickland, developed CPA to get around the nonlinear effects (OpticsCommunications 56 219). It works by taking theshort pulse and passing it through a pair of

gratings that stretch the pulse in time by a factor ofa 100 000. The gratings are arranged so that thelow- frequency component of the laser pulse travelsa shorter path than the high-frequency componentdoes, so the high-frequency component lagsbehind the low-frequency component and thepulse spreads out in time.

As the pulse is longer, its power is lower and itsenergy can then easily be increased by passing thepulse through a amplifier such as a titanium–sapphire crystal. The amplified pulse is thenpassed through a second pair of gratings thatreverse the dispersion – forcing the high-frequencycomponent of the laser pulse to travel a shorterpath and the low-frequency component to travel alonger path, so the pulse then “recombines” into ashort femtosecond pulse.

Shining light in the femtosecond regime

physicsworld.comNews & Analysis

12Physics World May 2010

accelerator. As the laser pro pagatesthrough the plasma, the electrons areexpelled around the laser pulse – justas a boat displaces water around it asit moves forward. As the electronsthen rush back in behind the laserpulse, they set up a trailing wave-likestructure known as a “wakefield” –like a water wave travelling behindthe boat. Other plasma electronstrap ped by these waves “surf” onthem behind the laser pulse pickingup energy and accelerating.

This technique allows laser light to accelerate electrons over a muchsmaller distance than conventionalparticle accelerators, which can betens of kilometres long. “Typically, wethink we can achieve electron ener-gies of about 10–20 GeV,” says Mou -rou. “So instead of building a 1 kmlin ear accelerator, we can instead usesomething that is only 1 m long.”

Mourou says that the Prague ELIcentre, which could also accelerateprotons for use in hadron therapy, will complement, rather than replace,other facilities that generate shortpulses of X-rays, such as the LinacCoherent Light Source (LCLS) at theSLAC National Accelerator Labor at -ory. But while LCLS, which is an X-rayfree-electron laser, can only producemonochromic radiation with pulsedurations of the order of 100 fs, ELIcould produce polychromatic ra di -ation of the order of a femtosecond orless, making it possible to take imagesof chemical reactions in real time.

“ELI is pushing the boundaries interms of testing this technology toprovide a range of applications,” saysJohn Collier, head of the high-power-lasers division at the Central LaserFacility at the Ruther ford lab.

Ripping atomsELI’s nuclear-physics facility in Ro -mania is set to be built in Ma gu rele,20 km south of Bucharest. The facil-ity will produce 10 PW beams that areshone directly onto a nucleus to studyhow the pulse affects nuclear energylevels. Researchers expect that thelaser pulse should be able to depositabout 1–10 keV on the nuc leus –enough to modify energy levels andforcing it to release a gamma ray. De -tecting this radiation would be proofthat researchers have affected thenucleus directly with laser light, thusallowing them to study nuclear trans -itions in more detail.

As for the Hungarian “attosecond”facility, it will use a 5 fs pulse with alaser beam of a few joules to generatepowers of the order of a petawatt. Thefacility, to be built in Szeged, 100 km

south of Budapest, will generate pulsesevery 1 ms that will be used to takesnap-shots on the attosecond scale(10–18 s) of electron dynamics in atoms,plasmas and solids. It will do this byshooting a femtosecond pulse of lightat a dense plasma target. In a processknown as “relativistic harmonic gen-eration”, the ionized plasma then givesoff so-called phase-locked radiation inthe ultraviolet and soft X-ray regimeat multiples of the frequency of theoriginal femtosecond pulse. Research -ers at ELI will then select the pulsesthat are generated in the atto secondregime with a filter and send them toexperimental stations to study mater-ials on the atomic scale.

Boiling the vacuumThe host for what is dubbed the“heart” of ELI – the “ultrahigh peakpower” facility – will not be knownuntil 2012, after some initial testingof technology for the three main fa -cilities is carried out. With an ex -pected completion date of 2018, thefacility will attempt to generate a100– 200 PW beam and use mirrors tofocus it onto an area of 1 µm2 in thehope of ripping open the fabric of thevacuum to produce particle and anti -particle pairs. “The vacuum is notsomething empty, but is full of activityof particles being created and de -stroyed,” says Mourou. “It defines allthe constants of physics.”

Quantum field theory states these“virtual particles” continually pop inand out of existence. It is predictedthat paired virtual particles could be -come real as they are torn apart by the pulse’s extremely strong electro-magnetic fields. How ever, this hap-pens too quickly to leave a trace andrequires light with an in tensity ofabout 1029 W cm–2. Known as the“Schwinger limit”, it is seven orders ofmagnitude larger than any currentlaser can achieve.

In its current design, ELI’s high-intensity facility will only be able toreach 1025 W cm2; however, Mannuel

Hege lich, project leader of short-pulse experiments and lasers at theLos Alamos National Laboratory inNew Mexico, says there are some newtheories being proposed that couldbring the Schwinger limit within ELI’sreach. “The vacuum has energy levelsand it would be great if we couldsomehow manage to modify them,”says Hegelich. Mourou also say theSchwinger limit could be matched bycolliding electron beams created bytwo lasers.

One of the technical challenges ofthe ultrahigh-peak-power facility willbe producing the vacuum itself. “Evenultrahigh-vacuum environments pro-duced by highly efficient pumps stillhave a few atoms floating around,”says Hegelich. One method would beto first shoot a laser pulse into thehigh-vacuum environment that wouldexpel all the particles and then quicklyfollow that up with a second high-powered pulse. “Technically, there isnothing that can’t be overcome withthe ultrahigh-peak-power facility,”says Hegelich. “It is more an engin -eering challenge that a physics one.”

One phenomenon that ELI shouldbe able to detect, which is predictedto happen at about 1023 W cm–2, is thevacuum becoming polarized and ex -hibiting optical phenomenon such as birefringence. Some theorists arealready proposing experiments for theultrahigh-peak-power facility such asa “matterless” double-slit experimentwhere the photons generated fromelectron and positron pairs annihil -ating form a double-slit diffractionpattern (Nature Physics 4 92).

As well as being a revolutionaryphys ics project that will test funda-mental theories and show how laserscould become the next particle accel-erator or collider, ELI is also tippingthe scales of Europe’s portfolio ofmajor infrastructures slightly moreeastwards. The presence of threemajor facilities in the Czech Repub -lic, Hungary and Romania will allowthese nations to attract researchersfrom abroad, as well as inspiring fu -ture generations of researchers.

“ELI will create new scientific com-munities and it will be a magnet for hi-tech companies,” says Sander, whonotes that for every euro spent on alarge infrastructure, 74 is given backto the economy. Yet for most physi-cists, it is ELI’s ultrahigh-power facil-ity, which will provide laser power farbeyond any existing today, that is themost exciting and eagerly awaited.“Within the next decade,” says Mou -rou, “we will be en tering a new para-digm in physics.”

Particle test-bedThe LASERIX laser at the Université Paris-Sud II has beentesting whether laserscan produce X-rays,as the Czech ELIfacility hopes to do.

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ELI will createnew scientificcommunitiesand it will be a magnetfor hi-techcompanies

physicsworld.com News & Analysis

13Physics World May 2010

Eensey, weensey unitsYou reported last month (April p3) on theefforts of Austin Sendek, a physics studentfrom the University of California, Davis, to establish the “hella” as an officialInternational System of Units (SI) prefixfor 1027. You also asked for suggestions onunit prefixes that go down to 10–27 – butsurely this is not difficult. I have longdeclared the “tini” (pronounced with an“ee” sound) to denote this quantity. Thisdesignation has the additional value of suggesting the subsequent two prefixes aswell: the “insi” (pronounced “eensey”) for10–30, to be followed closely by the “winsi”(pronounced “weensey”).

I have tried to think of prefixes thatwould come in on the high end beyond“hella” but unfortunately I could think ofnothing that could not be interpreted as arude word. Maybe I should not havelimited myself to the English language.B Todd HuffmanUniversity of Oxford, UKt.huffman1@ox.ac.uk

We already have the prefix “zepto” for10–21, but this is clearly a mistake for“zeppo”. Could we not have groucho, chico and harpo as prefixes for 10–27, 10–30and 10–33?Keith DoyleWalton on Thames, Surrey, UKkeith.doyle@lloyd-doyle.com

There is no need for a new “hella” prefix, asan extended set of SI prefixes has alreadybeen suggested by Victor Mayes. Writing in1994 in the Quarterly Journal of the RoyalAstronomical Society (35 569) Mayes’suggestion for 1027 was “nava”, from theSanskrit for nine (1027 = 10009). He also

suggested “sansa” for 1030 (san-shi beingChinese for “thirty”); “besa” for 1033 (besarmeans “great” in Malay-Indonesian) andso on up to “ultra” (Latin for “beyond,extreme”) for 1048. In a similar vein, Mayes’system assigned “tiso” (Arabic tis’a or“nine”) to 10–27; “vindo” (from Hindivindu, “a speck”) to 10–30 and “weto”(Maori wheto, “small”) to 10–33.

Using Mayes’ prefixes, the power of theSun can be written as 0.38 navawatt, while the mass of the galaxy is about220 catagrams (from the Spanish catorce or“fourteen”, denoting 1042 = 100014) andthe electron rest mass is 0.91 tisogram.J Keith AtkinUniversity of Sheffield, UKchet1@blueyonder.co.uk

Usually, the “most commented” articles onphysicsworld.com are those that concerncontroversial science policies, rather thanscience itself. Now and then, though, a scientificstory – in this case a proposed method forstoring wind energy in giant undersea bags –captures readers’ imaginations (“Spin-out putsnew spin on wind energy” 30 March; see alsop8). The idea would see pistons inside the bladesof giant wind turbines used to pump compressedair into storage balloons; on calm days, thestored air could be released to drive a set of turbines, thus ensuring a continuous supply of electricity. According to inventor Seamus Garvey, a similar scheme could helpstore surplus energy from nuclear reactors. Aninteresting notion, certainly – but is there acatch somewhere?

The proposal to use a bag system for storing“surplus energy from nuclear reactors” soundsfunny. It’s designed to store energy from unreliablesources, so I’d stick to that – it’s wind generatorsthat are causing mayhem on our energy grid, notnuclear plants.kasuha, Czech Republic

I agree that you should confine this system to wind,but I disagree that wind is causing havoc on thegrid. We also need to look at the environmentalimpacts, which will be significant if we startinstalling thousands of floating airbags at thebottom of the ocean. But then again, nothing isworse than coal and gas.gunslingor, US

You probably haven’t had enough blackoutscaused by wind turbines overloading the grid yet.Environmental or not (and I think these bags are farfrom environmentally friendly – they are going todamage quite large areas of sea bed), windturbines are causing many problems anddesperately need reliable means of energy storage.kasuha

High winds knocking down power lines is what’scausing mayhem on our grid, not wind generatorsor nuclear plants. Bring on the undersea bags!dratman, US

The bag might be a problem. I propose a simplersolution to store the air underwater: an open-endedcan or concrete caisson, sealed at the top andopen at the bottom. No moving parts.AlanM

Wouldn’t it be a lot easier to pump water up a hill?John Duffield, UK

Yes, pumping water uphill would work – but youhave to have a hill, and preferably a high one. I think an air-pump system would be moremaintenance-free than a pumping system that hasto deal with the corrosive effects of salt water.Newbeak

Is the weight of the piston inside the vanes the onlything supplying force to pump the air down to500 m below sea level?feet2thefire

I get a pressure of about 710 psi at 500 m. Youcould have a piston with a cross-section of0.1 square inches (just under 3/16 inch radius)weighing 71 lb. If the weight of the piston were theonly drive, it would need to be prohibitively long,possibly over 65 m if it were made of steel. Soprobably the plan would include some kind ofweight behind the piston. But the rotating partswould still need to seal against approximately710 psi, which is 49 atmospheres. This seems tome to be the killer for the engineering end of it.m.a.king, Canada

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The laser at 50

This issue of Physics World celebrates the 50th anniversary of the invention of the laserWhen Theodore Maiman eked out the first pulses of coherent light from a pink-ruby crystal on 16 May 1960, the 32-year-old engineer-turned-physicist at HughesResearch Laboratories in the US could not have imagined that the laser wouldbecome such a workhorse of physics – and so engrained in everyday life. Withinweeks, other physicists – notably those at Bell Laboratories – had reproducedMaiman’s success, with Bell Labs scientists then quickly notching up many otherlaser “firsts”, including the first gas lasers and the first continuously operatingruby lasers.

Lasers have gone on to be one of the outstanding success stories in physics. Theycan cool atoms, send data, mend eyes, sharpen astronomical images and probeindividual DNA molecules; they may even detect gravitational waves and triggerfusion. Hardly surprising then that, by our reckoning, some 14 physics Nobel prizeshave been awarded for achievements directly related – or linked – to lasers. Indeed,despite their use in the military, lasers do not suffer from an image problem, beingwidely regarded as a “good thing”.

This special issue of Physics World kicks off by reliving the laser’s first days and bycelebrating its impact on popular culture (think Goldfinger and laser-art shows)and everyday life (DVDs, laser pointers, bar-code scanners). We look at the tech-nological impact of lasers in fibre optics and at the quest for green-wavelengthlaser diodes that could let mobile phones project images onto any surface. Basicresearch gets a look-in, too – in terms of both ultrahigh power and ultrafast lasers.There is a timeline of laser history, while six experts predict where laser sciencewill go next. Online, don’t miss our video interviews with leading laser scientists,while the physicsworld.com blog reveals how we created our cover image and thephoto above. (As it turns out, there are some things lasers can’t do so well.)Matin Durrani, Editor of Physics World

The contents of this magazine, including the views expressed above, are the responsibility of the Editor. They do not represent the views or policies of the Institute of Physics, except where explicitly stated.

Physics WorldDirac House, Temple Back, Bristol BS1 6BE, UKTel: +44 (0)117 929 7481Fax: +44 (0)117 925 1942E-mail: pwld@iop.orgWeb: physicsworld.com

Editor Matin DurraniAssociate Editor Dens MilneNews Editor Michael BanksReviews and Careers Editor Margaret HarrisFeatures Editor Louise MayorWeb Editor Hamish JohnstonWeb Reporter James Dacey

Advisory Panel John Ellis CERN, Peter KnightImperial College London, Martin Rees University of Cambridge

Publisher Jo AllenMarketing and circulation Angela GageDisplay Advertisement Sales Edward JostRecruitment Advertisement Sales Chris ThomasAdvertisement Production Mark TrimnellArt Director Andrew GiaquintoDiagram Artist Alison Tovey

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There is one particular scene in H G Wells’ 1898 taleThe War of the Worlds that, if only I had remembered it,could have helped me to avoid a bad moment in mylaser lab in 1980. In the story – published long beforelasers came along in 1960 – the Martians wreak destruc-tion on earthlings with a ray that the protagonist calls an“invisible, inevitable sword of heat”, projected as if an“intensely heated finger were drawn… between me andthe Martians”. In all but name, Wells was describing aninfrared laser emitting an invisible straight-line beam –the same type of laser that, decades later in my lab,burned through a favourite shirt and started on my arm.

Wells’ bold prediction of a destructive beam weaponpreceded many others in science fiction. From the1920s and 1930s, Buck Rogers and Flash Gordonwielded eye-catching art-deco ray-guns in their spaceadventures as shown in comics and in films. In 1951 thepowerful robot Gort projected a ray that neatly dis-posed of threatening weapons in the film The Day theEarth Stood Still. Such appearances established laser-like devices in the popular mind even before they wereinvented. But by the time the evil Empire in Star WarsEpisode IV: A New Hope (1977) used its Death Starlaser to destroy an entire planet, lasers were a thing offact, not just fiction. Lasers were changing how we live,sometimes in ways so dramatic that one might ask,which is the truth and which the fiction?

Like the fictional science, the real physics behindlasers has its own long history. One essential startingpoint is 1917, when Einstein, following his brilliant suc-cesses with relativity and the theory of the photon,established the idea of stimulated emission, in which aphoton induces an excited atom to emit an identicalphoton. Almost four decades later, in the 1950s, the USphysicist Charles Townes used this phenomenon to produce powerful microwaves from a molecular me -dium held in a cavity. He summarized the basic process– microwave amplification by stimulated emission ofradiation – in the acronym “maser”.

After Townes and his colleague Arthur Schawlowproposed a similar scheme for visible light, TheodoreMaiman, of the Hughes Research Laboratories in Cali -

fornia, made it work. In 1960 he amplified red lightwithin a solid ruby rod to make the first laser. Its namewas coined by Gordon Gould, a graduate studentworking at Columbia University, who took the word“maser” and replaced “microwave” with “light”, andlater re ceived patent rights for his own contributionsto laser science.

Following Maiman’s demonstration of the first laserthere was much excitement and enthusiasm in the field,and the ruby laser was soon followed by the heliumneon or HeNe laser, invented at Bell Laboratories in1960. Capable of operating as a small, low-power unit,it produced a steady, bright-red emission at 633 nm.However, an even handier type was discovered two

Sidney Perkowitzis Candler Professorof Physics at EmoryUniversity, US, e-mailphysp@emory.edu.Also a science writer,his latest book –Hollywood Science:Movies, Science andthe End of the World –has just beenreissued in paperbackby ColumbiaUniversity Press

The first public reactions to lasers ranged from “Death ray!” to “Nice idea, but what good is it?”. Sidney Perkowitz reviews how lasers are now inextricably entwined in our lives, from everydayapplications to popular culture

From ray-gun to Blu-ray

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16Physics World May 2010

years later when a research group at General Electricsaw laser action from an electrical diode made of thesemiconductor gallium arsenide. That first laser diodehas since mushroomed into a versatile family of smalldevices that covers a wide range of wavelengths andpowers. The diode laser quickly became the most pre -valent type of laser, and still is to this day – accordingto a recent market survey, 733 million of them were soldin 2004.

Better living through lasersAs various types of laser became available, and differentuses for them were developed, these devices en teredour lives to an extraordinary extent. While Maiman was

dismayed that his invention was immediately called a“death ray” in a sensationalist newspaper headline,lasers powerful enough to be used as weapons wouldnot be seen for another 20 years. Indeed, the most wide-spread versions are compact units typically producingmere milliwatts.

A decade and a half after their invention, HeNelasers, and then diode lasers, would become the basisof bar-code scanning – the computerized registrationof the black and white pattern that identifies a productaccording to its universal product code (UPC). Theidea of automating such data for use in sales and inven-tory originated in the 1930s, but it was not until 1974that the first in-service laser scanning of an item with a

Do you expect me to talk?James Bond is heldcaptive by Goldfingerand his sci-fi red laser that can cutthrough gold.

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UPC symbol – a pack of Wrigley’s chewing gum –occurred at a supermarket checkout counter in Ohio.Now used globally in dozens of industries, bar codesare scanned billions of times daily and are claimed tosave billions of dollars a year for consumers, retailersand manufacturers alike.

Lasers would also come to dominate the way in whichwe communicate. They now connect many millions ofcomputers around the world by flashing binary bits intonetworks of pure-glass optical fibre at rates of terabytesper second. Telephone companies began installing optical-fibre infrastructure in the late 1970s and the firsttransatlantic fibre-optic cable began operating betweenthe US and Europe in 1988, with tens of thousands ofkilometres of undersea fibre-optic cabling now in ex -istence worldwide. This global web is activated by laserdiodes, which deliver light into fibres with core diam -eters of a few micrometres at wavelengths that arebarely attenuated over long distances. In this role, lasershave become integral to our interconnected world.

As lasers grew in importance, their fictional ver-sions kept pace with – and even enhanced – the reality.Only four years after the laser was invented, the filmGoldfinger (1964) featured a memorable scene thathad every man in the audience squirming: Sean Con -nery as James Bond is tied to a solid gold table alongwhich a laser beam moves, vaporizing the gold in itspath and heading inexorably toward Bond’s crotch –

though as usual, Bond emerges unscathed.That laser projected red light to add visual drama,

but its ability to cut metal foretold the invisible infraredbeam of the powerful carbon-dioxide (CO2) laser – thetype that once ruined my shirt. Invented in 1964, CO2lasers emitting hundreds of watts in continuous opera -tion were introduced as industrial cutting tools in the1970s. Now, kilowatt versions are available for usessuch as “remote welding” in the automobile industry,where a laser beam directed by steerable optics canrapidly complete multiple metal spot welds. High-power lasers are suitable for other varied industrialtasks, and even for shelling nuts.

Digital mediaAside from the helpful and practical uses of lasers,what have they done to entertain us? For one thing,lasers can precisely control light waves, allowing soundwaves to be recorded as tiny markings in digital formatand the sound to be played back with great fidelity. Inthe late 1970s, Sony and Philips began developingmusic digitally encoded on shiny plastic “compactdiscs” (CDs) 12 cm in diameter. The digital bits wererepresented by micrometre-sized pits etched into theplastic and scanned for playback by a laser diode in aCD player. In retrospect, this new technology deservedto be launched with its own musical fanfare, but thefirst CD released, in 1982, was the commercial album52nd Street by rock artist Billy Joel.

In the mid-1990s the CD’s capacity of 74 minutes ofmusic was greatly extended via digital versatile discs or digital video discs (DVDs) that can hold an entirefeature-length film. In 2009 Blu-ray discs (BDs) ap -peared as a new standard that can hold up to 50 giga-bytes, which is sufficient to store a film at exceptionallyhigh resolution. The difference between these formatsis the laser wavelengths used to write and read them –780 nm for CDs, 650 nm for DVDs and 405 nm for BDs. The shorter wavelengths give smaller diffraction- limited laser spots, which allow more data to be fittedinto a given space.

Although the download revolution has led to a de -cline in CD sales – 27% of music revenue last year wasfrom digital downloads – lasers remain essential to our

Lasers would come to dominate theway in which we communicate. They now connect many millions ofcomputers around the world byflashing binary bits into networks of pure-glass optical fibre at rates ofterabytes per second

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