An Introduction to Compton Scattering, Page 1



These pages are designed as a brief tutorial on Compton Scattering, and how we use it to produce x-rays.

An electromagnetic wave packet moves from left to right below (red).   The electron (yellow) is moving at relativistic speeds and collides with the electromagnetic wave.

LAB FRAME:

However, the electron sees a doppler up-shifted laser pulse in its rest frame.  The wavelength is contracted an amount proportional to the electron energy, as shown by the solid green line below.

ELECTRON FRAME:

In linear Compton scattering, the electron oscillates  in response to the electric field of the laser pulse at this higher frequency, but it's instantaneous energy is close to the initial energy (the perpindiular component of its motion is small).  As the electron oscillates, it radiates (dashed green line) in its rest frame at the same wavelength as the incident radiation.  Back in the laboratory frame however this radiated electromagnetic has received another doppler shift:

LAB FRAME:

This radiation can have a very small wavelength since it depends on the square of the electron energy (an additional factor of 0.25 is necessary to conserve energy and momentum simultaneously and has been ommitted from this simple calculation).  In our simple model, the blue radiation continues in the direction of the electron while the laser wave is reduced in amplitude and continues in its original direction.  The electron finishes the interaction with near its initial energy.

For example, using an electron beam with an energy of 5 MeV (or five million electron volts) in head-on collision with a near-infrared laser of 800 nm (or a photon energy of 1.55 eV) the Compton backscattered radiation has an energy of 600 eV, which is in the soft x-ray region.

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