Ultrafast Formation of Light Energy in Solid


Researchers from Kiel University used high-speed camera to examine ultrafast formation of light energy in a Fermi-dirac distributed electron gas

A team of researchers from the Institute of Experimental and Applied Physics at Kiel University (CAU), investigated the energy exchange of the electrons with their environment in real time. This allowed the team to distinguish individual phases of electrons. The team irradiated graphite with an intense, ultrashort light pulse and captured the impact on the behavior of electrons. According to the researchers, an in-depth understanding of the fundamental processes involved in ultrafast formation of light energy in solid plays a major role in future for applications in ultrafast optoelectronic components. The research was published in the journal Physical Review Letters on December 19, 2018.

Fermi gas is a basic model to describe the behavior of electrons and considers electrons in the material to be a gaseous system. This helps to describe interactions of electrons with each other. To follow the behavior of electrons in real time, the team developed an experiment that investigates whether a material sample when irradiated with an ultrafast pulse of light leads to simulation of electrons for a short period. Moreover, a second, delayed light pulse emits some of these electrons from the solid. A detailed analysis of these phenomenon enables to draw conclusions regarding the electronic properties of the material followed by the first stimulation with light. The team used a special camera to capture the distribution of introduced light energy through the electron system.

According to the researchers, the new system has high temporal resolution of 13 femtoseconds. The extremely short duration of the light pulses allows to film live ultrafast processes. In the current experiment, the team irradiated a graphite sample with a short, intense light pulse of around seven femtoseconds duration. The team found that the photons disturbed the thermal equilibrium of the electrons. The equilibrium describes a condition in which a precisely-definable temperature is consistent amongst the electrons. The team captured the behavior of the electrons, until a balance was restored after around 50 femtoseconds.