Happy 50th birthday to the laser

[Prometheus]

Next week sees the 50th birthday of an invention that was initially described as a "death ray", or – more charitably – "a solution looking for a problem". For most, the development of the laser – and with it the ability to generate an intense, narrow beam of light of a single wavelength – was a matter of complete indifference. Yet today, lasers can be found everywhere, from laboratories at the cutting edge of quantum physics to supermarket checkouts and hospitals.
Lasers read and write DVDs, guide commercial aircraft, carry out dental repairs, squirt information down optical fibres, print documents, cut metal for tools, make nifty pointers for slide shows, among a host of other uses. But as with many other great ideas, their journey to prominence was very long and very slow.
It was Einstein himself who came up with the idea, back in 1917, building on his earlier realisation that light was made up of tiny particles called photons. Physicists had already worked out that electrons in atoms could occupy many different energy levels. The further away a level is from the heart of the atom, the higher its energy. Blast atoms with the right amount of energy and their electrons jump up to higher, more excited, levels. As they fall back to lower levels, they shed the energy in the form of photons: a big jump yields blue light, a little one gives red.
In an ordinary light bulb, light is emitted from the atoms in the filament this way – a phenomenon known as "spontaneous emission". But Einstein envisaged a different, more orderly form of light – hence the term "laser", which stands for Light Amplification by Stimulated Emission of Radiation.
Suppose that you have already excited the electrons in a material's atoms. Einstein realised that if you stimulated those atoms with photons of equal energy to the ones the electrons were about to emit, you would create an avalanche of electrons that sent out photons of the same wavelength, travelling in the same direction.
The first practical consequence of this came in 1954, when Charles Townes and his students at Columbia University in New York showed how stimulated emission could be harnessed at microwave frequencies. The result was a "maser" – like a laser, but using microwaves instead of visible light.
When it came to extending the maser's range of operation to the much higher frequencies needed to make a laser, however, there were significant problems. In the end, a solution was found by an outsider in the race to make a working model, Ted Maiman, who based the device on an artificial crystal of pink ruby. Initially, he had a hard time convincing his bosses at the Hughes Research Laboratories in Malibu, California, to let him work on the project at all. When Hughes eventually announced the laser's invention, in 1960, it was greeted by headlines that dubbed it a "death ray" that was "brighter than the sun".
Unfortunately Maiman fell victim to the philistine attitude of the establishment, submitting the manuscript announcing his discovery to a leading journal only to see it turned down. Townes would claim the Nobel Prize for its invention in 1964, the same year that James Bond was almost sliced in two by a laser in Goldfinger ("Do you expect me to talk?" "No, Mr Bond, I expect you to die".)
Today, however, Maiman is getting his due. That first laser – which emitted a beam for the first time on May 16, 1960 – will be brought out of a safe-deposit box to be the star attraction at a conference at Simon Fraser University in Vancouver at the end of this week. The museum at MIT has also marked the anniversary with a laser show set to what its British director, John Durant, calls "Pink Floyd-ish" music, and events are planned in – among other places – Naples, Kiev, Hong Kong, Buenos Aires, Damascus and the Royal Academy of Engineering in London (for more details, see LaserFest | Home)
Today, the most vital application of lasers is probably their use in communication, most particularly the fibre-optic cables that keep our phone networks running (the original work was done by Professor Charles Kao at the Standard Telecommunications Laboratory in Harlow, for which he shared a Nobel last year). Yet we are constantly discovering new ways to exploit the distinctive properties of laser light.
In California, scientists at the National Ignition Facility are about to concentrate 192 laser beams on a pellet of hydrogen fuel. If it works, the power of the lasers will crush the hydrogen atoms together to ignite nuclear fusion, creating a microscopic star – and with it, some people believe, the prospect of limitless energy. Recent reports in New Scientist have outlined how lasers can zap artillery shells, remove varnish from old paintings, clear space junk or even create clouds on demand.
As for what the future will bring, Colin Webb, Emeritus Professor of Physics at the University of Oxford and chairman of Oxford Lasers Ltd, predicts that the increasing precision and efficiency of lasers will soon enable us to work on a scale of billionths of a metre, to create more efficient microchips and new kinds of materials. "One thing that 50 years of experience in this field has taught me," he says, "is that there will be new applications which we can't even begin to speculate on today."
Roger Highfield is the Editor of 'New Scientist'
Happy 50th birthday to the laser, the 'death ray' at every supermarket till - Telegraph