Multiphoton momentum trasfer

1. Oct 27, 2011

1Keenan

Hi everybody,

I'm reading P. Gibbon book "Short Pulse Laser Interaction with Matters", and I'm having a problem.
Describing the ejection of an electron from a focused laser beam the book says, on pag 39, that "the kinetic energy of the electron is given by:

$\Delta$U=($\gamma$-1)mc$^{2}$

This energy is extracted from electromagnetic field via multiphoton momentum transfer."

I would like to know the demostration of that formula, since no clue is given in the book.

Thanks for helping

2. Oct 27, 2011

kith

ɣmc² is the total energy of a relativistic massive particle. When you subtract the rest energy mc² from this, you get the relativistic kinetic energy.

This is just an energy conservation consideration and has nothing to do with the concrete mechanism of how this energy is extracted from the em field.

3. Oct 28, 2011

1Keenan

I get confused because of the multiphoton stuff...

Thank you very much