An artistic rendering of two black holes colliding, from which gravitational waves were detected by the LIGO experiment. Credit: SXS Project
When scientists announced last year that they’d detected gravitational waves from the distant collision of two black holes, they confirmed Albert Einstein’s 100-year-old theory that gravity, packaged in waves, travels across space and time.
The 900-member global science team responsible for the discovery, honored with the Nobel Prize in Physics Oct. 3, is the Laser Interferometer Gravitational Wave Observatory (LIGO) collaboration. Earlier this year, LIGO added new members from Colorado State University. The CSU team will provide critical coating technology to increase the sensitivity of LIGO, and to advance knowledge of coating architectures for future LIGO generations.
Menoni group tapped for LIGO
The CSU group of the LIGO Scientific Collaboration is led by University Distinguished Professor Carmen Menoni, professor in the Department of Electrical and Computer Engineering. Her team is charged with improving key aspects of the observatory’s hardware – in particular, coatings on the mirrors that reflect laser beams. Leading the development and testing of the coatings is Le Yang, a graduate student in the Department of Chemistry, where Menoni holds a dual affiliation; and postdoctoral researcher Mariana Fazio.
The LIGO experiment is conducted in two, identical facilities – one in Louisiana and the other in Washington – and each is an L-shaped, 2.5-mile-long (4 kilometer) interferometer. The interferometer splits a laser beam in two, and the twin beams hit mirrors that bounce the beams back and forth. Changes in length of the interferometers’ arms create dark-and-light patterns. Scientists model this “interference” pattern to determine whether a gravitational wave has passed through.
Vibrations limit wave detection
The scientists’ ability to detect the waves is limited by many sources of noise, among them atomic vibrations in the thin-film coatings on the mirrors; the vibrations mask the waves and render them undetectable. Menoni’s team is tasked with uncovering what’s causing the vibrations, and to mitigate it. If they are successful, the LIGO interferometers should become sensitive to more gravitational signals originating further from Earth.
Menoni is a well-known expert in making multilayer oxide coatings with specific optical properties through a process called ion beam sputtering. Her CSU group will experiment with new kinds of coatings for the LIGO mirrors, which will be tested by partners at Caltech, MIT and Stanford. Their goal is to make coatings that reduce wave-masking vibrations for the present and future interferometers operating in the near infrared end of the spectrum.
“Right now, the sensitivity of LIGO interferometers is limited by the coatings in the test masses,” Menoni said. “Our efforts will aim to increase the sensitivity of the detectors by a factor of 10. It’s a very interesting problem from the physics and optics point of view. We have a great opportunity here to make a dent in a very difficult problem.”
The original architects of LIGO, Rainer Weiss, Kip Thorne and Barry Barish, were awarded the Nobel Prize in Physics Oct. 3 for their work in the discovery of gravitational waves.