Laser setup probes nanoarchitected structures

A team by ISN PI Prof. Carlos Portela has developed a new technique called Laser-Induced Resonant Acoustic Spectroscopy (LIRAS) that uses ultrafast laser pulses to induce vibrations in samples — similar to the way a hammer induces vibrations when striking a bell — without actually touching the sample. The vibrations can be used to characterize the effects generated when materials are impacted, sheared, or undergo other stresses. Using LIRAS to characterize architected metamaterials provides a huge increase to the speed of evaluating the properties of structures — allowing many samples to be pulsed in a matter of minutes — and can establish a “signature” pattern of how a particular architecture responds, enabling even faster comparison to other structures. The technique could also be used to inspect other types of metamaterials (e.g., acoustic structures), further extending its utility.
A metastructure bends left and right, changing colors from light green to deep purple as the top leans increasingly out of alignment.

A new MIT technique uses a laser to safely scan a microscopic tower of metamaterial, inducing vibrations that can then be captured with a second laser and analyzed to deduce the structure’s dynamic properties, such as stiffness in response to impact. Image: courtesy of the researchers.

One of several vertical metastructures is interrogated by a simulated laser pulse

This optical micrograph shows an array of microscopic metamaterial samples on a reflective substrate. Laser pulses have been digitally added, depicting pump (red) and probe (green) pulses diagnosing a sample in the center. The LIRAS technique sweeps through all samples on the substrate within minutes. Credits: Courtesy of the researchers

This image shows electron microscope micrographs of polymeric metamaterial samples, approximately 50 micrometers wide and as tall as about twice the width of human hair, whose properties were determined via the LIRAS technique. Pump and probe lasers were aimed at the flat tops to induce vibrations throughout the samples. Image: Courtesy of the researchers