By Josh Perry, Editor
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Researchers at the Institute of Experimental and Applied Physics at Kiel (Germany) University (CAU) used an ultrafast camera system to study the energy exchange of irradiated graphite electrons and the environment in real time.

With the ultrafast system in the Physics Centre at the CAU, the behaviour of electrons can be filmed live. (Jürgen Haacks, CAU)

According to a report from the university, the researchers irradiated the graphite sample with a pulse of light to stimulate the electrons, while a second, delayed pulse releases some of the electrons from the material.

The key to filming this ultrafast process is a camera system developed at CAU that has a temporal resolution of 13 femtoseconds (a femtosecond is one quadrillionth of a second), one of the fastest cameras in the world.

“In their current experiment, the research team irradiated a graphite sample with a short, intense light pulse of only seven femtoseconds duration,” the article explained. “In the experiment, the impacting light particles - also called photons - disturbed the thermal equilibrium of the electrons. This equilibrium describes a condition in which a precisely-definable temperature prevails amongst the electrons. The Kiel research team then filmed the behavior of the electrons, until a balance was restored after about 50 femtoseconds.”

Researchers witnessed different phases in the electrons, from irradiated electrons absorbing light energy then passing that electrical energy to other electrons and eventually into other atoms, where the energy was converted to heat.

The research was recently published in Physical Review Letters. The abstract stated:

“Time- and angle-resolved photoelectron spectroscopy with 13 fs temporal resolution is used to follow the different stages in the formation of a Fermi-Dirac distributed electron gas in graphite after absorption of an intense 7 fs laser pulse.

“Within the first 50 fs after excitation, a sequence of time frames is resolved that are characterized by different energy and momentum exchange processes among the involved photonic, electronic, and phononic degrees of freedom.

“The results reveal experimentally the complexity of the transition from a nascent nonthermal towards a thermal electron distribution due to the different timescales associated with the involved interaction processes.”