But how fast do electrons oscillate to produce extreme ultraviolet radiation in a solid? This is revealed by the frequency of the emitted radiation and the theoretical interpretation of the experiments. “We have a strong indication that the laser pulses force the electrons to perform extremely fast oscillations of tens of Petahertz (1015 Hz) frequencies inside the crystal ,” Goulielmakis explains. “In fact, this is the fastest electric current ever generated in a solid, and the emitted radiation from these oscillations allow us to peer into the dynamics of this extremely fast motion.”

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