Using electrons to observe extremely strong magnetic fields traveling close to the speed of light
Various edistributions after traveling through the 10,000 T strength fields generated on the surface of a solid by the ultraintense laser HERCULES (. Schumaker et al., Phys. Rev. Lett. 2013). (b) The HERCULES laser, in the Center for Ultrafast Optical Science at the University of Michigan is the world’s most intense laser.
In the January edition of Physical Review Letters, Will Schumaker and colleagues demonstrated imaging of extremely strong magnetic fields (10,000 times that of the strongest bar magnet!) in a surface plasma with a size of only tens of microns expanding at close to the speed of light, by observing the deflections of relativistic electrons. Intense laser pulses interacting with solid surfaces can create energetic plasmas for research into numerous areas, for example: inertial confinement fusion; compact particle accelerators; radiation sources; scaled astrophysical experiments. Such plasmas are highly complex and can evolve on very short time scales, so that measurement of plasma parameters such as density and magnetic field strength requires a time resolved measurement.
Using the 30 femtosecond (30×10-15 seconds) duration laser pulse from the HERCULES laser, which is considered to be the world’s most intense laser, located in the Center for Ultrafast Optical Science at the University of Michigan, Ann Arbor, the authors focused intense light on to a thin metal foil to generate a rapidly expanding surface plasma. To “probe” the magnetic fields generated within this plasma, they used a second short laser pulse focused into atmospheric density gas. This generates a burst of relativistic electrons by “surfing” them on the electric plasma wave generated behind the pulse, like the wake of a boat, which have a temporal duration comparable to that of the laser pulse. Having propagated through the magnetic fields generated in the laser-solid interaction, the spatial distribution of electrons reflects the magnetic field structure at the time when they were deflected. By adjusting the delay between the pulse hitting the solid target and the probe electron pulse, the authors can effectively make a “movie” of the plasma evolution.
W. Schumaker, N. Nakanii, C. McGuffey, C. Zulick, V. Chyvkov, F. Dollar, H. Habara, G. Kalintchenko, A. Maksimchuk, K. A. Tanaka, A. G. R. Thomas, V. Yanovsky, and K. Krushelnick
Phys. Rev. Lett. 110, 015003 (2013) Published January 2, 2013
Also highlighted at Physics.aps.org