Research Could Improve Laser-Based Manufacturing Technique

Engineers have discovered details about the behavior of ultra-fast laser pulses that may lead to new applications in manufacturing, diagnostics, and other research.

The use of ultra-fast laser pulses creates features and surface textures in metals, ceramics, and other materials for applications including the manufacture of solar cells and biosensors. The lasers pulse at durations of 100 femtoseconds, or quadrillionths of a second, cause electrons to reach temperatures greater than 60,000oC during the pulse duration. The pulses create precise patterns in a process called cold ablation, which turns material into a plasma of charged particles.
 

This series of high-speed images shows how plasma expands when exposing material to ultra-fast laser pulses. Purdue researchers have discovered details that could help to harness the technology for applications in manufacturing, diagnostics, and research. (Yung Shin, Purdue University, School of Mechanical Engineering)

Images taken with a high-speed camera show tiny mushroom clouds eerily similar in appearance to those created in a nuclear explosion. The clouds expand outward at speeds of 100 to 1,000 times the speed of sound, within less than one nanosecond. However, new findings reveal that an earlier cloud forms immediately before the mushroom cloud, and this early plasma interferes with the laser pulses, hindering performance, says Yung Shin, a professor of mechanical engineering and director of Purdue University’s Center for Laser-Based Manufacturing.

Finding a way to eliminate the interference caused by the early plasma could open up new applications in manufacturing, materials and chemical processing, machining and advanced sensors to monitor composition, and chemical and atomic reactions on an unprecedented scale, he says.

Researchers used experiments and simulations to study the phenomenon. Research papers about the work were published online in Applied Physics Letters and in the journal Physics of Plasmas. Doctoral student Wenqian Hu, Shin, and mechanical engineering professor Galen King wrote the papers.

Mechanical engineering doctoral student Wenqian Hu, who graduated this past fall, works on a complex optical setup that is part of research at Purdue University to uncover details about the behavior of ultra-fast laser pulses. The technology may have new applications in manufacturing, diagnostics, and other research. (Purdue University photo/Mark Simons)

“We found the formation of early plasma has very significant bearing on the use of ultra-short pulse lasers because it partially blocks the laser beam,” Shin states. “The early plasma changes the optical properties of air, but the mechanism is still largely unknown.”

The researchers studied the early plasma by:

• Tracking the movement of millions of individual atoms in the plasma
• Observing how the laser beam travels in space and interacts with plasma
• Using a laser pump probe shadowgraph, a technique in which one laser ablates a material, producing the early plasma, and a second laser, fired perpendicular to the first, enables study of the cloud. The shadowgraph technique implements a series of optical elements and mirrors.

Funding for the research is by the National Science Foundation.

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