An Off-the-Shelf Thermal Camera Could Let LIGO See 33 Million Light-Years Farther

One of the most expensive instruments in physics may get a substantial upgrade from a camera you can order online.

The problem researchers at the University of California, Riverside set out to solve is old and stubborn. LIGO, the Laser Interferometer Gravitational-Wave Observatory, works by bouncing a laser between mirrors suspended at the ends of four-kilometer vacuum tubes and watching for changes in the distance between them smaller than a proton. To reach that precision it runs laser power approaching a megawatt. Its mirrors — among the purest optical components ever manufactured — still absorb a sliver of that light. The absorbed energy heats the glass and warps its surface by a few nanometers. That warp distorts the beam, and the distortion quietly erodes the detector's sensitivity.

Engineers have known about the effect for years. What they have lacked is a good real-time measurement of it. Existing Hartmann wavefront sensors give a partial picture, and correcting a distortion you can only partly see is guesswork.

The team, led by Jonathan Richardson, took a different route: point a commercially available thermal imaging camera at each mirror from outside the interferometer and photograph its surface temperature. Those temperature maps, calibrated against the existing Hartmann sensors, can be matched uniquely to a finite-element model of the mirror. That yields the mirror's complete internal thermal state — which in turn allows full-aperture reconstruction of the wavefront and provides direct error signals for real-time correction.

The projected gain is not marginal. The team estimates the technique could improve the strain sensitivity of the coming LIGO A+ upgrade by as much as 31%, extending the range at which the detector can spot two neutron stars merging by roughly 33 million light-years on average. Because the volume of space surveyed scales with the cube of the distance, a 31% reach improvement translates into more than double the observable volume — and therefore roughly double the rate of detected events.

What makes the result unusual within the collaboration is how little it demands. LIGO instrumentation upgrades typically mean custom-fabricated optics, new suspension hardware, or years of vacuum-system work. This one needs a camera mounted outside the vacuum envelope and software to interpret what it sees. Richardson has noted that a hardware upgrade requiring no new technology is close to unheard of for the observatory.

The method is expected to be built into the design of Cosmic Explorer, the proposed next-generation U.S. gravitational-wave observatory, whose 40-kilometer arms would face the same thermal problem at even higher laser powers. For a field that has logged 390 black-hole and neutron-star collisions since 2015, doubling the survey volume is the difference between cataloguing rare events and doing population statistics on them.