Simultaneous imaging of K-α radiation and coherent transition radiation from relativistic-intensity laser-irradiated solid target plasmas

Laser acceleration of hot electrons and their transport through 12–32 μm thick Ti foils was explored experimentally using two complementary diagnostics, a bent crystal imaging the Ti Kα emission and optical imaging of the coherent transition radiation (CTR) produced by the exit of the hot electrons from the foil. The spatial extent of the hot electron production measured by these two diagnostics is dramatically different. Electrons producing CTR emerge in a spot of less than 7 μm and appear to maintain a high degree of collimation during transport through the foil while electrons that produce Kα emission appear to diverge to sizes of 50–100 μm as viewed from the back surface of the foil. These results indicate that there is a large difference in the transport of the highest energy electrons contributing to CTR signal as compared with the bulk of the hot electron population generating Kα signal.

► We present experiments on energetic electron transport in Titanium foils. ► A laser drove the electrons to relativistic speeds, using an intensity >1019 W/cm2. ► Simultaneous Kα X-rays and CTR imaging removes uncertainties due to laser deviation. ► The electrons emitting CTR clearly transport through the material uniquely.