A laser is a device that emits a focused beam of coherent light. Coherent means all the waves are in phase, same frequency, same direction. That is why laser light is so concentrated. It does not spread out like a flashlight beam. It can cut steel, read a DVD, or measure the distance to the moon.

The first laser was built in 1960 by Theodore Maiman. It used a ruby rod and a flash lamp. Since then, lasers have become ubiquitous. Supermarket scanners, laser printers, fiber optic communications, and surgical tools all rely on them. They are also in every CD and Blu-ray player.

Types of lasers

• Gas: helium-neon, carbon dioxide
• Solid-state: ruby, Nd:YAG
• Semiconductor: laser diodes in pointers and drives
• Fiber: used in telecommunications
• Excimer: used in eye surgery

Lasers are classified by hazard. Class 1 is safe. Class 4 can burn skin and eyes. Laser pointers are usually Class 2 or 3R. Shining one at an aircraft is a federal crime. The beam is small, but the consequences are not.