lasers

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Lasers produce narrow, intense beams of monochromatic light.

Ordinary visible light is a combination of waves of different frequency and wave length (and so colour) that are ‘out of phases’ meaning the crests and troughs don’t match.

A laser beam is just a special ray of light that has a few extra properties which make it special.

All the waves in a laser beam are at the same frequency (and wavelength). This means the light is monochromatic.

The light waves are all in phases with each other – the troughs and crests line up, increasing the amplitude, so producing an intense beam.

The waves in a laser beam are said to be coherent because they have a fixed phase’s difference.

Lasers have low divergence – the beam is narrow, and it stays narrow, even at a long distance from the light source.

Cd use lasers to read digital information.

The surface of a cd has a pattern of billions of shallow pits cut into it. The areas between the pits are called lands.

A lasers shone onto a cd is reflected back from the shiny bottom surface as it spins around the player.

The beam is reflected from a land and a pit slightly differently – the difference is picked up by a light sensor. These defences are then converted into electrical signal. The pits and lands themselves don’t represent the digital on and offs. It’s actually a change in the reflected beam which represents on and off.

An amplifier and a loudspeaker then convert the electrical signals into sound of the right pitch.