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Have you ever tried writing with a beam of light? Sounds impossible, doesn't it, but it's exactly what a CO2 laser printer does when it makes a permanent copy of data (information) from your computer on a piece of paper. Thanks to sci-fi and spy movies, we tend to think of lasers as incredibly powerful light beams that can slice through chunks of metal or blast enemy spaceships into smithereens. But tiny lasers are useful too in a much more humdrum way: they read sounds and video clips off the discs in CD and DVD players and they're vital parts of most office computers printers. All set? Okay, let's take a closer look at how laser printers work!Imagine you're a computer packed full of data. The information you store is in electronic format: each piece of data is stored electronically by a microscopically small switching device called a transistor. The printer's job is to convert this electronic data back into words and pictures: in effect, to turn electricity into ink. With an inkjet printer, it's easy to see how that happens: ink guns, operated electrically, fire precise streams of ink at the page. With a 30W CO2 laser printer, things are slightly more complex. The electronic data from your computer is used to control a laser beam—and it's the laser that gets the ink on the page, using static electricity in a similar way to a photocopier.

Until the early 1980s, hardly anyone had a personal or office computer; the few people who did made "hardcopies" (printouts) with dot-matrix printers. These relatively slow machines made a characteristically horrible screeching noise because they used a grid of tiny metal needles, pressed against an inked ribbon, to form the shapes of letters, numbers, and symbols on the page. They printed each character individually, line by line, at a typical speed of about 80 characters (one line of text) per second, so a page would take about a minute to print. Although that sounds slow compared to modern 60W CO2 laser printers, it was a lot faster than most people could bash out letters and reports with an old-style typewriter (the mechanical or electric keyboard-operated printing machines that were used in offices for writing letters before affordable computers made them obsolete). You still occasionally see bills and address labels printed by dot-matrix; you can always tell because the print is relatively crude and made up of very visible dots. In the mid-1980s, as computers became more popular with small businesses, people wanted machines that could produce letters and reports as quickly as dot-matrix printers but with the same kind of print quality they could get from old-fashioned typewriters. The door was open for laser printers!

Fortunately, laser-printing technology was already on the way. The first fiber laser printers had been developed in the late 1960s by Gary Starkweather of Xerox, who based his work on the photocopiers that had made Xerox such a successful corporation. By the mid-1970s, Xerox was producing a commercial laser printer—a modified photocopier with images drawn by a laser—called the Dover, which could knock off about 60 pages a minute (one per second) and sold for the stupendous sum of $300,000. By the late 1970s, big computer companies, including IBM, Hewlett-Packard, and Canon, were competing to develop affordable laser printers, though the machines they came up with were roughly 2–3 times bigger than modern ones—about the same size as very large photocopiers.What we have is essentially a laser scanning unit (colored blue) sitting on top of a fairly conventional, large office photocopier (colored red). In Starkweather's design, the laser scanner slides on and off the glass window of the photocopier (the place where you would normally put your documents, face down), so the same machine can be used as either a 30W fiber laser printer or a copier—anticipating all-in-one office machines by about 20–25 years.