Ultrafast metal dynamics revealed


Rebecca Pool

Wednesday, March 15, 2017 - 11:30
Image: Imaging femtosecond laser-induced surface structural dynamics in metals
US-based researchers have developed a technique to visualize, for the first time, the complete evolution of micro- and nanoscale structural formation on a material’s surface, both during and after the application of a laser pulse.
Femtosecond laser-material interactions have been extensively investigated but a clear understanding of even the simplest morphological response has eluded researchers.
SEM images of microstructural changes on a material's surface after irradiation with femtosecond laser pulses [Guo Lab]
Given this, Professor Chunlei Guo and colleagues, from the Institute of Optics at the University of Rochester, developed a high contrast scattered-light optical imaging method to capture exactly how laser irradiation alters a material’s surface.
“After we determined that we could drastically alter the property of a material through creating tiny structures in its surface, the next natural step was to understand how these tiny structures were formed,” highlights Guo. “This is very important because after you understand how they’re formed you can better control them.”
The ultrafast pump-probe imaging set-up uses an amplified Ti:sapphire laser system to generate femtosecond pulses for inducing surface structure formations on a metal target.
Femtosecond imaging setup [Guo Lab]
During a femtosecond laser pulse, the beam is split in two: one pump beam is aimed at the material target to induce the micro- and nano-structural changes.
Meanwhile a second probe beam provides stroboscopic light to illuminate the process ready for recording with a CCD camera. 
Crucially, the technique opens a window on the entire process, from the moment a laser hits the material to melting, transient surface fluctuations, and resolidification resulting in permanent micro- and nanostructures.
Video: Imaging at the speed of light.
The researchers can pattern a one-inch by one-inch metals sample in around an hour.
“We worked very hard to develop this new technique,” highlights Guo. “With the scattered light pulsing at femtosecond time intervals, we can capture the very small changes at an extremely fast speed."
Researchers hope the method will open the door to myriad ultrafast studies including melting, crystallography, fluid dynamics, and even cell activities.
Research is published in Light: Science and Applications, a Nature publication.
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