'Rubber Laser' Material Advances Sensor Technology

A rubberlike material that emits coherent light without mirrors — even while it's being stretched — could be used in remote sensors or as a tunable light source.

Liquid crystal elastomers (LCEs) can curl up, bend, twist, wrinkle and stretch when exposed to light, heat, gases and other stimuli. Because they are so responsive, they could be used for biophotonics applications in artificial muscles and blood vessels, actuators, sensors, plastic motors and drug-delivery systems.

Researchers from Kent State University and Kyoto Institute of Technology in Japan developed the LCEs, building upon the earlier work of Kent professor Peter Palffy-Muhoray and his colleagues. In 2001, they demonstrated the use of liquid crystals to bounce laser light back and forth inside a cavity without the need for any external mirrors. However, accurate control of the laser emission frequency was not possible then.

A liquid crystal elastomer is used as a mechanically tunable, mirrorless laser. Courtesy of Kent State University

The liquid crystal acts as both the distributed cavity host and the active medium. Simple optical pumping of such a sample results in low-threshold, mirrorless lasing at the band edges.

Liquid crystal elastomers can change their shape when the orientational order of the constituents is altered by changing the temperature, applying a field or introducing impurities. As a sensor, it could be used to measure strain, which is just a small change in length, or stress, which is force per area.

"In principle, it could be put into a shoe to measure shear stress on a diabetic foot, and it could be interrogated by an optic fiber,” Palffy-Muhoray said. “A pulse of light could be sent in the fiber, and the color of the returning light from the laser emission would carry information about the strain. Similarly, remote equipment could be monitored — by measuring stress, strain, temperature and presence of chemicals — by optic fibers using light."

The work was published in Nature (doi: 10.1038/srep17739 [open access]) and was funded by the U.S. National Science Foundation and Japan Society of Promotion of Science.