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## Main Question or Discussion Point

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:

[itex]\Delta[/itex]U=([itex]\gamma[/itex]-1)mc[itex]^{2}[/itex]

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

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:

[itex]\Delta[/itex]U=([itex]\gamma[/itex]-1)mc[itex]^{2}[/itex]

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