PDA

View Full Version : Coherence



AriAstronomer
2010-Aug-04, 10:10 AM
So I'm wondering about Coherence. I've been to wiki sites and I know the basics of it, but my teacher's explanation left me a bit confused, dropping terms like 'interference' and 'Add the amplitudes and square it' that are not found anywhere online (as far as I can see). Specifically we were talking about Coherent Photons. I would like to know what Coherent photons are, and although I know they are probably used for a wide range of things, maybe an example or two of what the use of them are.

Thanks a bunch!

mugaliens
2010-Aug-05, 04:39 AM
"Two waves are said to be coherent if they have a constant relative phase." There are several levels of coherence, however, from temporal coherence (monochromacity) to spatial coherence (direction) spectral coherence (when light of waves with different frequencies combines to form a pulse, i.e. the waveshave a fixed relative phase-relationship) and polarization coherence (when the electric fields are all ascillating in the same plane).

Ken G
2010-Aug-09, 06:33 PM
Specifically we were talking about Coherent Photons. I would like to know what Coherent photons are, and although I know they are probably used for a wide range of things, maybe an example or two of what the use of them are.

The key thing that waves do that nothing else does is exhibit constructive and destructive interference. The oval office in the White House is built to reflect sound waves from one focus so they constructively interfere at the other focus. Sound cancelling headphones, on the other hand, create destructive interference, so that you cannot hear background sound. The oval office doesn't create more sound, and the headphones don't absorb sound, they just control the constructive and destructive interference. It all works because waves have a frequency and a phase.

AriAstronomer
2010-Aug-10, 09:21 AM
Thankya guys. Helpful as always.