# Power in beam of light given amplitude

1. Dec 20, 2012

### Cspeed

I would like to calculate the power of a beam of light once I know the electric field amplitude. For example if I know the amplitude along a line from -1 meter to +1 meter every 0.5 m is [1, 2, 2.5, 2, 1 V/m], how can I find the power from this is? Is there enough info? (it's in vacuum/air) Thank you.

2. Dec 20, 2012

### Staff: Mentor

Energy density is proportional to the squared amplitude (see Wikipedia for example), and power is just average energy density times the speed of light. Don't forget the magnetic component, which is 50% of the total power.

3. Dec 20, 2012

### Cspeed

Thanks, but I'm not sure still. I knew that power was proportional to the square of amplitude, but I'm hoping to get a figure in watts. I see that I need H as well. But how does this all fit in to my 1-D scenario?

4. Dec 20, 2012

### Staff: Mentor

You get W/m^2 - what else did you expect? If the source emits radiation uniform in space, you can multiply that with the corresponding sphere surface area to get the total power.