laser-produced relativistic plasmas
Since the work of Albert Einstein in 1905, we know that matter cannot move faster than light. When we try to accelerate particles beyond, their mass increases rapidly preventing their acceleration beyond the speed of light. Particles moving close to speed of light are called “relativistic”. This is commonplace in big accelerators, but it is only since recently that one can create highly relativistic electrons in small laboratories. The enabling technology has been ultrashort laser pulses, which can produce electric field strengths of a megavolt per micrometer or more. If matter is exposed to such fields by focusing the pulses on a gas of atoms or a solid target, atoms are stripped of their electrons. The freed electrons are then accelerated close to the speed of light within one oscillation of the laser field. The result is highly relativistic electrons, much more heavy than their counterparts in atoms, molecules or metals.
LAP’s table-top high-intensity lasers
produce billions of relativistic electrons in tiny, micrometer-sized volumes. These electrons are then 10 – 1000 times heavier than normal electrons. The mass of the ionized atoms does not change significantly, because they remain slow owing to their large mass. This mixture of “heavy” electrons and ions forms a relativistic plasma. Outside laser laboratories, this unusual state of matter occurs only close to black holes in cosmos. The laser wave creating such a plasma drives electrons in the forward direction. As a consequence, electrons can be blown out of a thin solid foil or be separated from ions in a gas of atoms, creating thereby a wake plasma wave behind the laser pulse, the longitudinal field of which can also efficiently accelerate electrons.
produce billions of relativistic electrons in tiny, micrometer-sized volumes. These electrons are then 10 – 1000 times heavier than normal electrons. The mass of the ionized atoms does not change significantly, because they remain slow owing to their large mass. This mixture of “heavy” electrons and ions forms a relativistic plasma. Outside laser laboratories, this unusual state of matter occurs only close to black holes in cosmos. The laser wave creating such a plasma drives electrons in the forward direction. As a consequence, electrons can be blown out of a thin solid foil or be separated from ions in a gas of atoms, creating thereby a wake plasma wave behind the laser pulse, the longitudinal field of which can also efficiently accelerate electrons.
The mass of a particle increases with its velocity according to m=\gamma\,m_0 where m_0 is the rest mass of the particle and \gamma=1/\sqrt{1-v^2/c^2}
is the relativistic factor of mass increase, v and c are the speed of the particle and the speed of light in vacuum, respectively. As the speed of the particle approaches that of light, \gamma approaches infinity, making the particle infinitely massive to avoid acceleration beyond the speed of light.
If the electric field E of a light pulse becomes so strong that its electric force F_E=e\,E can accelerate an electron close to the speed of light, the magnetic force F_B = e(v\times B) of the same wave becomes as large as the electric force, and first accelerates the electron perpendicularly to the laser propagation but the equally strong magnetic force bends the trajectory of the electron forward, resulting in a relativistic beam of electrons moving along the laser beam.
If the electric field E of a light pulse becomes so strong that its electric force F_E=e\,E can accelerate an electron close to the speed of light, the magnetic force F_B = e(v\times B) of the same wave becomes as large as the electric force
, and first accelerates the electron perpendicularly to the laser propagation but the equally strong magnetic force bends the trajectory of the electron forward, resulting in a relativistic beam of electrons moving along the laser beam.
