Building Better Mirrors to Lead LIGO Into the Future

Center for Gravitational-Wave Physics and Astronomy alumnus Nicholas Demos (BS ’17) now designs and tests new mirror materials for better gravitational-wave detection at MIT.

This image shows coating defects after a test for annealing temperatures.

This photo shows defects that appeared after annealing (baking) the coating on a 2-inch silica substrate.

Nicholas Demos (BS ’17) has enjoyed math since his grandfather taught him how to count by twos and threes before he started kindergarten. Years later, he was mesmerized by an episode of Carl Sagan’s “Cosmos,” launching his fascination with physics and space. While he says he slept through most of his first-period high school physics class, Demos enjoyed watching doctoral-level physics lectures in his spare time.

Pausing his undergraduate career to run his family’s business didn’t deter his interest. When he returned to Cal State Fullerton’s College of Natural Sciences & Mathematics, he decided to pursue physics as a major and research in gravitational waves, a young field poised for a dramatic discovery.

“I took an introduction to physics course with [Associate Professor of Physics] Geoffrey Lovelace, a researcher at the [now Nicholas and Lee Begovich] Center for Gravitational-Wave Physics and Astronomy, and I did well. During office hours, he offered me an opportunity to do research with him over the summer,” says Demos, who had started thinking about pursuing a doctoral degree in physics. “I had never heard of gravitational waves, but I was excited to do research.”

About a year later, on Sept. 14, 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) detectors recorded gravitational waves for the first time, confirming Einstein’s prediction from 100 years earlier that changes in gravity create waves of space and time. The source of the waves was also a completely new discovery: two black holes, more than 1 billion light years away from Earth, each around 35 times as massive as the sun, orbiting around each other at a quarter the speed of light. These black holes crashed into each other, forming a new black hole with 67 times the mass of the sun. The crash released three times the mass of the sun as gravitational-wave energy, according to Einstein’s famous equation E = mc2.

“I used to tease the faculty a lot before that happened, saying ‘IF we detect gravitational waves’ and ‘IF they’re real,” Demos says, with a laugh. “But it was a lot of fun and really exciting since there was only a small group of people working on this. Right after it happened, I joined the LIGO Scientific Collaboration, in which you get privileged information, but the detection happened in September and we couldn’t say anything until the following February, so it was a tough secret to keep!”

A colorful, reflective coating sample on 1-inch fused silica substrate
A coating sample on 1-inch fused silica substrate – an example of a sample Demos’ team uses in experiments to measure and characterize coating properties.
Alumnus Nick Demos works inside the vacuum chamber
Alumnus Nick Demos (left) works inside the vacuum chamber in the clean room of the LIGO Lab at MIT with Satoshi Tanioka (right), a visiting student from Sokendai University in Japan.
Alumnus Nick Demos works inside the vacuum chamber in the clean room of the LIGO Lab at MIT
Alumnus Nick Demos (left) works inside the vacuum chamber in the clean room of the LIGO Lab at MIT with Satoshi Tanioka (right), a visiting student from Sokendai University in Japan.
Two monitors show images of a laser beam.
Screens connected to cameras monitor the shape and quality of the laser beam during the experiment.
Equipment for sample analysis
In the upper left is the vacuum chamber that houses many components of the experiment. The table on the outside is where the researchers collect and measure the laser light that exits from the vacuum chamber’s view port.
Equipment for sample analysis
The orange and black fiber feed-through gets the laser light into the vacuum chamber.
An upgraded piece of equipment with motorized components
This cavity upgrade means both the arms and the sample mirror mount are motorized and can be controlled from a computer outside the vacuum, allowing researchers to change the shape of the cavity on the fly.
A close-up of mirror equipment
A few of the mirrors that need to be aligned just right to get the image out of the vacuum chamber.
A super-close image of mirrors that detect laser beams
The view through several mirrors to where a beam spot will be in the future.

A Key Role in Revolutionary Research

Demos’ undergraduate work involved numerical supercomputer simulations of crashing black holes, which create ripples in space-time. It was his first experience with computer programming in a real way, and he learned high-level programming languages like Linux, Python, and Mathematica, which would prove very useful in later graduate studies.

“My professors at Cal State Fullerton were fantastic at giving me opportunities to participate in conferences, give talks, and present posters, so I had a huge resume and a lot of valuable experience when I started looking at graduate programs,” Demos says. “I decided I wanted to stick with LIGO, and Caltech and MIT have LIGO labs funded by the National Science Foundation. I got into both and chose MIT because I really liked the program and because my girlfriend was accepted to a school nearby.”

With his new advisor, Matthew Evans, the MIT MathWorks Professor of Physics, he launched into a new aspect of LIGO, designing and testing new mirror materials for better gravitational-wave detection.

LIGO “listens” for gravitational waves, vibrations in space-time caused by the densest objects in the universe – black holes and neutron stars – falling into a collapsing orbit and spinning until they collide. Functioning like a massive ruler, LIGO then measures the stretching and squeezing of all parts of space in the wave’s path using a device called a laser interferometer. The time it takes light to travel between suspended mirrors is measured with high precision using controlled laser light.

“One of the limiting factors is thermal noise, caused by the movement of atoms on the surface of the mirrors,” Demos says. “The mirror surfaces are like the ends of a ruler. When atoms that make up the coatings on the mirror surfaces jiggle around, it is like the ends of your ruler jiggling around while you are trying to make a precise measurement. Some materials have less thermal noise than others, and we’re working on testing different mirror materials and ways to layer materials to reduce thermal noise.”

Evans and MIT Research Scientist Slawomir Gras developed the only apparatus able to quickly test full mirror samples, instead of just a single layer or a few layers of the materials used to coat the mirrors, and Demos runs these tests.

“Other people have tried different methods of measuring, but my advisors at MIT came up with this clever tabletop optic experiment, a very sensitive setup,” Demos says. “Designing and thinking about the types of materials needed to create low-thermal-noise mirrors and then testing them and characterizing their properties is vital to the future of LIGO. Any potential coating upgrade for LIGO will likely need to be characterized in our lab before being installed.”

Coatings are painted on glass to create these mirrors, and as more layers are added, more light is reflected. By making a 2D map, the researchers can learn how substrate imperfections can propagate to the top. Their apparatus can also measure different beam sizes to tease out the underlying properties of the materials contributing to thermal noise.

In recognition of his work, Demos recently received a $70,000 fellowship from MathWorks, a software company that produces mathematical computing programs. He says he was honored to receive the prestigious award, and it takes the pressure off securing funding for his stipend and lab expenses for a full year.

A photo of Nick Demos and girlfriend Alyssa Garcia
Nick Demos (left) and girlfriend, Alyssa Garcia (right), are both Cal State Fullerton 2017 physics alumni.

Looking Toward the Future

Though he never could have imagined exactly where he’d be today, Demos says he’d advise any physics or science student who wants to pursue a doctoral degree to get involved in research as soon as possible.

“If you are interested in gravitational waves, from the faculty to the instruments, Cal State Fullerton is a powerhouse.”
Nicholas Demos (BS ’17)

“High school is not too early to begin reaching out to physics departments and expressing interest in research opportunities. If you are already in college, talk to professors in your department,” he says. “With faculty involved in the full spectrum of gravitational-wave research, from astrophysics theory to the instrumentation, Cal State Fullerton is a powerhouse and a place I’d recommend for anyone interested in the field.”

Demos is excited about the future of his field. In the short term, he is thrilled about playing a key role in the coating decisions for the mirrors that will soon be used for LIGO. Long term, he says there are third-generation gravitational wave detectors being planned for 10 to 15 years from now and he’s eager to see, and play a part in developing, the technology that will go into them.

“Right now, we can see as far as a merger of two neutron stars, but in the future we hope to be able to see every binary black hole and neutron star collision that ever happened in the universe.”

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