Gravitational waves, tiny ripples in spacetime caused by cosmic collisions like merging black holes, are almost impossibly faint. Detecting them requires LIGO (Laser Interferometer Gravitational-Wave Observatory), one of the most sensitive instruments ever built.
However, there’s a catch. To see farther and catch weaker signals, LIGO needs more powerful lasers, but stronger lasers slightly bend the mirrors, and even tiny bends smaller than a proton can block the signals.
A team of researchers has developed a new system called FROSTI to fix this problem, enabling LIGO and future observatories to explore the cosmos more deeply than ever before.
“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,” Jonathan Richardson, one of the researchers and a physicist at the University of California, Riverside, said.
How does FROSTI work?
LIGO’s mirrors are 34 cm wide, 20 cm thick, and weigh 40 kg. When megawatt-level laser beams pass through them, about five times the current power used at LIGO—the mirrors heat unevenly, creating tiny bumps and dips that reduce sensitivity.
FROSTI (FROnt Surface Type Irradiator) corrects these distortions by projecting controlled heat patterns onto the mirror surface using a ring of heater elements. This carefully reshapes the mirror, smoothing out warps while keeping the added noise extremely low.
“Despite its icy name, FROSTI works by carefully heating the mirror’s surface, but in a way that restores it to its original optical shape,” the UC Riverside team notes.
The system works inside LIGO’s ultra-high vacuum without contaminating the mirrors. Tests showed the prototype can handle very high laser power, correct complex distortions, and tolerate slight misalignment of the beam.
“Using thermal radiation, it creates a custom heat pattern that smooths out distortions without introducing excess noise that could mimic gravitational waves,” the UC Riverside team added.
Currently, FROSTI works on 40-kg mirrors, but it can be scaled up for the heavier 440-kg mirrors planned for future detectors like Cosmic Explorer.
Expanding our view of the universe
With FROSTI, gravitational-wave observatories can detect fainter and more distant events, increasing the observable volume of the universe by roughly ten times.
This could allow astronomers to capture millions of black hole and neutron star mergers, as well as various other mysterious cosmic events that remain undetectable at present. Such observations would greatly enhance our understanding of extreme phenomena in the universe.
“The current prototype is just the beginning. 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 said.
The study is published in the journal Optica.