does it mean extract electrons from the out put of laser beem
Did you do a google search on this already? If you did, you would have seen numerous references, better than what most of us can explain on here, with clear figures and animation, even!
Try it. Search "Free electron laser" or FEL
A free electron laser uses a high-energy electron beam and an array of magnets arranged as an "undulator". As the electrons pass through the varying magnetic fields their paths bend in a carefully calculated pattern ... and with each bending motion light is emitted - the light continues on along the open path.
It is not a laser in the usual sense; it lacks the cavity, and doesn't use stimulated emission. It is more like a baby synchrotron light source. They are very high-tech, and very expensive research tools.
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