Lasers have found applications almost beyond number. In manufacturing, infrared carbon dioxide lasers cut and heat-treat metal, trim computer chips, drill tiny holes in tough ceramics, silently slice through textiles, and pierce the openings in baby bottle nipples. In construction the narrow, straight beams of lasers guide the laying of pipelines, drilling of tunnels, grading of land, and alignment of buildings. In medicine, detached retinas are spot-welded back in place with an argon laser's green light, which passes harmlessly through the central part of the eye but is absorbed by the blood-rich tissue at the back. Medical lasers are also used to make surgical incisions while simultaneously cauterizing blood vessels to minimize bleeding, and they allow doctors to perform exquisitely precise surgery on the brain and inner ear.
Many everyday devices have lasers at their hearts. A CD or DVD player, for example, reads the digital contents of a rapidly spinning disc by bouncing laser light off minuscule irregularities stamped onto the disc's surface. Barcode scanners in supermarkets play a laser beam over a printed pattern of lines and spaces to extract price information and keep track of inventory.
Pulsed lasers are no less versatile than their continuous-beam brethren. They can function like optical radar, picking up reflections from objects as small as air molecules, enabling meteorologists to detect wind direction or measure air density. The reflections can also be timed to measure distances—in some cases, very great indeed. A high-powered pulsed laser, aimed at mirrors that astronauts placed on the lunar surface, was used to determine the distance from Earth to the Moon to within 2 inches. The pulses of some lasers are so brief—a few quadrillionths of a second—that they can visually freeze the lightning-fast movements of molecules in a chemical reaction. And superpowerful laser pulses may someday serve as the trigger for controlled fusion, the long-sought thermonuclear process that could provide humankind with almost boundless energy.