Summer intern learns at intersection of chemistry and optical fiber

Mary Ann Cahoon’s journey to an internship with the National Ignition Facility (NIF) & Photon Science Directorate at Lawrence Livermore National Laboratory (LLNL) began at the Corning Museum of Glass in upstate New York.

“I was a high school student, considering studying chemical engineering in college,” she said. “But that museum opened me up to the world of optical materials. I was fascinated.”

This led Cahoon, a native of St. Louis, to attend the Missouri University of Science and Technology in the ceramic engineering program. She’s now three years into a Ph.D. in materials science and engineering at Clemson University in South Carolina and is currently spending the summer interning with LLNL's Fiber Technologies Group.

This summer, Cahoon has been working at the intersection of chemistry and glass optical fiber fabrication, which is also her dissertation topic. Clemson operates an optical fiber fabrication facility where researchers develop custom optical fibers for applications like high-power lasers, similar to research done at LLNL. She learned about the internship through her adviser, professor John Ballato, who has collaborated on research with Fiber Technologies Group Leader Mike Messerly and Optical Materials Science & Technology Program Director Tayyab Suratwala.

NIF&PS intern Mary Ann Cahoon, a Clemson University Ph.D. student, at the bottom of LLNL’s fiber draw tower, where she spends much of her time. Photos by Jason Laurea.

“Mary Ann’s experience with Clemson’s fiber draw tower has been a great benefit,” Messerly said. “Everyone does things a little differently, so it’s good to learn from one another.”

Her summer project takes a wet chemistry approach to create nanoparticles suspended in a sol-gel solution, which are used to create the core layer in an optical fiber.

“We’re trying to put in a new material into an optical fiber, which means developing a new processing method from scratch,” Cahoon said. “The goal is to make a robust optical fiber.”

When light is confined and propagated through fiber, the material composition of the core has a great effect on the characteristics of the light. Understanding and controlling the core chemistry helps with fiber design for specific applications like sensors and lasers.

“We aim to use highly refractive index glasses of the type that Mary Ann is investigating in our optical fiber waveguides,” Messerly said. “In the past, these parts were based on fused silica, but we want to consider other materials.”

In the lab of Jungmin Ha of the Optical Science Materials and Technology group within NIF&PS, Cahoon runs experiments that tweak the processing method and evaluate the effects of different factors.

Intern Mary Ann Cahoon (center), her mentor David Feng (left), and engineer William Moore (right) demonstrate the array of optical fibers created at the fiber draw tower.

“My background is in wet chemistry and Mary Ann’s is in chemical deposition, so it’s a good collaboration,” Ha said. “Her thoughtful questions help me think deeply about my process.”

It’s an iterative process with more failures than successes, but that’s what intrigues Cahoon.

“When things don’t work, that’s when it gets interesting,” she said. “I then explore why the experiment didn’t go exactly as I expected and then apply what I learn to the next experiment.”

She’s especially excited about this project because it’s something that’s never been done before. “I think that gives you some creativity because you have the freedom to see what happens, rather than following a prescribed routine,” she said.

That curiosity has helped Cahoon succeed at LLNL. “She’s very curious and diligent, which is a great combination,” said David Feng, her mentor. “She’s always asking the right questions.”

In addition to her research project, she’s enjoyed socializing with other interns. On the weekends, she’s enjoyed hiking trips with other interns, visiting Bay Area highlights like Muir Woods, Pinnacles National Park and Point Lobos.