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Electrons travel faster than light in glass

Using ultrashort laser pulses, physicists have been able to generate hot electrons that travel faster than the speed of light in a piece of glass 1 .

This opens a new avenue for understanding several areas of high-energy science ranging from laser-driven fusion to developing advanced radiation sources that have potential applications in the industrial and medical fields.

Ultrashort laser pulses, each one lasting a millionth of a billionth of a second (a femtosecond), can accelerate electrons on a solid surface to near light speeds. However, little is known about the fate of such short-lived electrons inside the solid.

An international research team, including physicists from the Tata Institute of Fundamental Science in Mumbai, India, shone ultrashort laser pulses on a glass target in a vacuum chamber placed on top of a table. The laser ejected electrons inside the glass and instantly kicked them to speeds approaching that of light.

After travelling small distances at speeds faster than that of light, the electrons dissipate energy in the glass medium. They emit Cherenkov radiation, light produced by charged particles when they pass through an optically transparent medium at speeds greater than the speed of light. They emit such radiation throughout the length of the target.

The fast electrons last 2000 times longer than the laser pulses. Theoretically speaking, this is much longer than the time they should take to traverse the target. This research is a significant step towards developing a method that will help understand hot-electron transport through solids, the researchers say.



  1. Shaikh, M. et al. Mapping the damping dynamics of mega-ampere electron pulses inside a solid. Phys. Rev. Lett. 120, 065001 (2018)

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