# How does a photo detector detect?

1. Apr 16, 2006

### einstein2603

How does a photo detector detect? Can you also tell me where you got the info from.

thanks

einstein2603

2. Apr 16, 2006

### Hootenanny

Staff Emeritus
Hello again einstein,

All 'photodetectors' operate using the photoelectric effect (or variants of). Basically, the photoelectric effect can be explained using quantum physics. Have you heard of the wave-particle duality of light? The photoelectric effect was the first source of firm evidence for the particle nature of light. Basically, light can be considered as a massless particle called the photon which has an energy of $E = hf$. This site is very useful and should have all the information you need. If you have any questions, you can post them here

http://hyperphysics.phy-astr.gsu.edu/hbase/quacon.html#quacon

Regards,
~Hoot

3. Apr 16, 2006

### andrevdh

Basically the photons causes the material that it falls on to become conductive - electrons (or their counterparts - holes) are generated (freed) from their bound states and become part of the sea of free charges that can flow in the material - that is the charge carriers are raised to a higher energy level by absorbing the energy from the photon. This increase in conductivity is sensed as an increase in current through the detector by a circuit connected to it. See for instance http://en.wikipedia.org/wiki/Photodiode

Last edited: Apr 16, 2006