Electron injector and free electron laser

A free electron laser comprising:

• an electron injector comprising:
• a support structure arranged to support a photocathode;
• a beam delivery system arranged to direct a beam of radiation from a radiation source onto a region of the photocathode thereby causing the photocathode to emit a beam of electrons;
• an adjustment mechanism operable to change the region of the photocathode which is illuminated by the radiation beam;
• and
• a steering unit operable to apply a force to the beam of electrons to alter its trajectory such that the electrons become substantially coincident with an axis of the electron injector;
• a particle accelerator operable to accelerate the beam of electrons to relativistic speeds;
• and
• an undulator operable to cause the relativistic electrons to follow an oscillating path thereby causing them to stimulate emission of coherent radiation.

A method of producing an electron beam using an electron injector, the method comprising:

• directing a beam of radiation onto a region of a photocathode thereby causing the photocathode to emit a beam of electrons;
• changing the region of the photocathode which is illuminated by the radiation beam;
• and
• applying a force to the beam of electrons to alter its trajectory such that the electrons become substantially coincident with an axis of the electron injector.

A method for producing radiation comprising:

• producing an electron beam comprising:
• directing a beam of radiation onto a region of a photocathode thereby causing the photocathode to emit a beam of electrons;
• changing the region of the photocathode which is illuminated by the radiation beam;
• and
• applying a force to the beam of electrons to alter its trajectory such that the electrons become substantially coincident with an axis of the electron injector;
• accelerating the beam of electrons to relativistic speeds;
• and
• causing the relativistic electrons to follow an oscillating path thereby causing them to stimulate emission of coherent radiation.