special issue

The laser at 50: A cultural historyphysicsworld.comPhotolibraryTEK Image/Science Photo LibraryUPC 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 installingoptical-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 versionskept 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 –Lasers would come to dominate theway in which we communicate.They now connect many millions ofcomputers around the world byflashing binary bits into networksof pure-glass optical fibre at rates ofterabytes per second18though 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 (CO 2 ) laser – thetype that once ruined my shirt. Invented in 1964, CO 2lasers 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. Highpowerlasers 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 discsor 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 gigabytes,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 forBDs. The shorter wavelengths give smaller diffractionlimitedlaser 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 ourPhysics World May 2010