Surprising optics breakthrough could transform our view of the Universe

LIGO is an observatory that measures gravitational waves -- tiny ripples in spacetime created by massive accelerating objects such as colliding black holes. It was the first facility to directly detect these waves, providing strong support for Einstein's Theory of Relativity. Using two 4-km-long laser interferometers located in Washington and Louisiana, LIGO senses incredibly small disturbances, giving scientists a new way to study black holes, cosmology, and matter under extreme conditions.

LIGO relies on mirrors that are among the most carefully engineered components in modern science. Each mirror is 34 cm across, 20 cm thick, and weighs about 40 kg. To detect distortions in spacetime that are smaller than 1/1,000th the diameter of a proton, these mirrors must be held almost perfectly still. Even tiny vibrations or environmental noise can drown out the faint gravitational-wave signals that LIGO is trying to detect.

"At the heart of our innovation is a novel adaptive optics device designed to precisely reshape the surfaces of LIGO's main mirrors under laser powers exceeding 1 megawatt -- more than a billion times stronger than a typical laser pointer and nearly five times the power LIGO uses today," said Richardson, an assistant professor of physics and astronomy. "This technology opens a new pathway for the future of gravitational-wave astronomy. It's a crucial step toward enabling the next generation of detectors like Cosmic Explorer, which will see deeper into the universe than ever before."

FROSTI: precision thermal control for LIGO mirrors

FROSTI, short for FROnt Surface Type Irradiator, is a precision wavefront control system designed to cancel out distortions produced when intense laser light heats LIGO's optics. Existing systems can only make relatively coarse corrections, but FROSTI uses a more advanced thermal projection method to apply fine, higher-order adjustments to the mirror surfaces. This level of control is essential for the more demanding performance requirements of future detectors.

Despite its icy name, FROSTI operates by warming the surface of the mirror in a very controlled way that returns it to its ideal optical shape. By using thermal radiation, the system projects a carefully tailored heat pattern onto the mirror. This smooths out optical distortions while avoiding extra noise that could be mistaken for real gravitational-wave signals.

Why better optics matter for gravitational-wave astronomy

Gravitational waves were first detected by LIGO in 2015, marking the beginning of a new era in astronomy. To fully exploit this new way of observing the universe, however, upcoming detectors need to see more distant events and measure them with greater clarity.

"That means pushing the limits on both laser power and quantum-level precision," Richardson said. "The problem is, increasing laser power tends to destroy the delicate quantum states we rely on to improve signal clarity. Our new technology solves this tension by making sure the optics remain undistorted, even at megawatt power levels."

With this approach, the new technology is expected to expand the observable gravitational-wave universe by a factor of 10. That increase in reach could allow astronomers to detect millions of black hole and neutron star mergers across cosmic history, and to study them with unprecedented detail.

Looking Ahead: LIGO A# and Cosmic Explorer

FROSTI is expected to be a key component of LIGO A#, a planned upgrade that will act as a testbed for the next-generation observatory known as Cosmic Explorer. The current prototype has been demonstrated on a 40-kg LIGO mirror, but the same principles can be scaled up and adapted to the much larger 440-kg mirrors proposed for Cosmic Explorer.

"The current prototype is just the beginning," Richardson said. "We're already designing new versions capable of correcting even more complex optical distortions. This is the R&D foundation for the next 20 years of gravitational-wave astronomy."

Richardson conducted the research in collaboration with scientists at UCR, MIT, and Caltech.

The work was supported by a grant to Richardson from the National Science Foundation.