Scientists use perfectly timed lasers pluses to pause silicon melting

Researchers from the University of California and the University of Kassel have developed a novel laser technique that can pause the ultra-fast melting of silicon by precisely timing two laser pulses separated by 126 femtoseconds. Typically, a single high-energy laser pulse causes silicon to undergo non-thermal melting, where atoms lose their ordered crystalline structure in less than a trillionth of a second without significant heating. However, by splitting the laser energy into two pulses and synchronizing them accurately, the team was able to halt this melting process mid-way, creating a metastable form of silicon that retains most of its original electronic properties, including a slightly reduced band gap. Using ab initio molecular dynamics simulations, the researchers showed that the first pulse initiates atomic motion, while the second pulse disrupts this motion to effectively "freeze" the atoms in place, preventing the loss of crystalline order. This metastable state also exhibited cooler and more stable atomic vibrations (phonons) than expected, indicating enhanced control over atomic behavior.