How are the binary numbers represented in the ridges of the CD?

How are the binary numbers represented in the ridges of the CD?

In principle, the binary numbers could be written as the presence or absence of ridges (i.e. a 1000 nanometer long ridge could be a 1 while a 1000 nanometer long flat area could be a 0). However, this technique has technical problems. The main problem is that the number “0” would be a long flat region (16 adjacent flat regions would be one 16000 nanometer flat region). If the flat region became too long, the CD wouldn’t be able to follow the track any more. So an encoding scheme is used to make sure that ridges and flat areas are never too long. They use a length-encoding scheme, where ridges of different lengths correspond to a short group of binary bits. Furthermore, a very extensive error correcting arrangement makes sure that the music can be read even if a great many bits are unreadable. About 25% of the CD’s surface is dedicated to this error correcting information.

Why do you need to separate the different polarizations of light?

Why do you need to separate the different polarizations of light?

Any light wave can be described in terms of horizontally and/or vertically polarized light. For most things, these two polarizations are unimportant. But when light reflects from surfaces or passes through certain materials, these polarizations become important. The charges in surfaces and materials do not always respond equally to the two polarizations of light. The two polarizations may even travel through very different paths (e.g. in the polarization beam splitter).

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.