Yes, there really is a laser in a Laser Printer (Photos)

The actual laser assembly from an Apple LaserWriter 16/600

The actual laser assembly from an Apple LaserWriter 16/600

Ever wonder why the word “laser” is in the term “Laser Printer”? Is it an actual laser, or is this just some gimmick to sell more printers?

To find out, I painstakingly disassembled the guts of a 1990’s era Apple Laserwriter 16/600 printer. My approach: keep removing hunks of metal, motors and plastic until I found the laser. This activity served to kill an otherwise unoccupied afternoon during a break in business school. Click for photos and a detailed breakdown.

Indeed, there is a laser, which is part of an assembly of mirrors, motors and lenses:

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So whats going on here? A laser printer, much like a photocopier, works by creating a static charge on a rotating drum. This drum is then exposed to fine dust which collects where the charge is, and then the dust is fused onto the paper by heating coil. In a regular office photocopier, a system of lenses takes the reflection of your original document and shines this light on the drum. In a laser printer, this task is handled by a small laser.

Here is the close-up of the laser:

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This laser is pointed at a spinning octagonal mirror:

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As you can see, the mirror part is on the edges of this spinning disc.

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My guess is that this scatters the laser light against the a series of lenses which project the light on the drum.

Software inside the printer must generate a signal of laser pulses based on where the disk is known to be at any given instant. I guess the principal is very much like the scanning electron beam in a television set. The dot moves so quickly that it effectivly paints an image against the drum.

Originally published here.