How does a laser diode work?

How does a laser diode work?

A laser diode resembles a light emitting diode, in which electrons flowing across a p-n junction (in a diode) find themselves in conduction levels of the p semiconductor, with lots of excess energy. These excited electrons give up their excess energy by emitting light and they drop down into empty valence levels with much less energy. In a laser diode, the region in which this energy release occurs is a very narrow channel with mirrored ends. Instead of emitting their light spontaneously, the electrons experience stimulated emission. Light bounces back and forth between the ends of the channel and is amplified as it passes new excited electrons. Because all of the light produced by a laser diode emerges from one end of this very narrow channel, it experiences severe diffraction and spreads out into a wide, cone-shaped beam. To convert this cone of light into a narrow beam, a converging lens is usually attached to the diode laser’s housing and this lens bends the beam into a fine pencil of light. Most laser diodes operate in the red or infrared portion of the spectrum, although some laser diodes that emit blue light have recently been developed.

Will light going in two directions in the same space create destructive interfer…

Will light going in two directions in the same space create destructive interference?

In general, the answer is no—there won’t be large regions of space in which the two light waves cancel one another. That’s because, while the electric fields from the two waves do add to one another at each moment, those fields go in and out of phase with one another very rapidly as the waves pass and the end result is that they do not interfere with one another over broad expanses. However, there can be points or surfaces in space at which the electric fields from the waves at least partially cancel for extended periods of time and at which there is destructive interference. These points and surfaces are often observed in experiments with single frequency laser beams.

How does alternating current affect the laser? Does it make the laser reverse?

How does alternating current affect the laser? Does it make the laser reverse?

A diode laser will only emit light (lase) when current flows through it in the proper direction. It is, after all, a diode and only conducts current in one direction. But small fluctuations in current do affect the light emission. If you run a modest current through a laser diode, so that it emits a steady stream of light, and then begin to modulate that current up and down slightly, the light emitted by the laser will modulate up and down slightly, too. In this manner, you can send sound or other information over a laser beam. This technique is useful as a private means of communicating over long distances. Only someone who can “see” the blinking laser beam can detect the information that it contains.