While this is not a traditional electronics project, it makes use of one of the most phenomenal success stories of modern electronics, the semiconductor laser diode. The first laser diodes were demonstrated in 1962, but they could be operated only in brief pulses and emitted only invisible near-infrared radiation. Decades were required before reasonably priced, continuously operating (CW) laser diodes became available. They emitted just one wavelength: red. In recent years frequency doubling crystals have been widely used to transform the infrared emitted by high-power laser diodes into brilliant green beams. This and other new developments have provided laser diodes that emit across the visible spectrum.
While today's principle application for laser diodes is in laser read/write systems, they have many other important applications in sensing, intrusion alarms and both optical fiber and free-space communication. They are also useful for making miniature laser light shows and laser art, the topic of this Circuit Recipe.