Big Ideas Lab Podcast looks back at the laser guide star

Late one evening about 30 years ago, a beam of light shot into the sky from Lawrence Livermore National Laboratory (LLNL), creating confusion and awe in the surrounding community. It wasn’t a UFO, as some people feared, but the start of a revolution in astronomy.

That beam of a light was a demonstration of the laser guide star, which would go on to light up the night sky and open doors to profound mysteries of the cosmos. The latest episode of LLNL’s Big Ideas Lab Podcast delves into this fascinating history. Listen on Apple or Spotify.

To the naked eye, stars appear to twinkle. This is not through any action on the part of the celestial objects, but rather is due to atmospheric turbulence — the blustery mixing of Earth’s atmosphere — that the light rays pass through on their long journey to the eyes of night watchers and the lenses of telescopes.

The laser guide star creates an artificial star by shooting a laser into the sodium layer of the atmosphere, about 90 kilometers up. At a wavelength of 589 nanometers (billionths of a meter), the laser excites the sodium, which fluoresces in return.

This star provides a reference point for an advanced optics system, which uses it to inform a computer-controlled deformable mirror that cancels out the effects of atmospheric turbulence to create a sharp image.

Many astronomical discoveries of the last 30 years would not have been possible without the laser guide star. The black hole discovery that won the 2020 Nobel Prize in Physics is just one example.

The genesis of the laser guide star began in the 1980s. Claire Max, then a physicist at LLNL and now a professor emerita at the University of California, Santa Cruz, was part of a JASON advisory group study that assessed the feasibility of using a green laser to create an artificial beacon to find and track satellites. That concept was not feasible, but it led to a new idea — using a yellow laser at 589 nanometers wavelength to measure turbulence high in the sky. But that yellow laser didn’t yet exist.

“On a lovely spring day, Herb Friedman, a laser engineer, and I were eating lunch together and talking about how no one had even tried to build one of these laser guide stars,” recalls Max. “And after we finished our lunch, we looked at each other and said, ‘Well, if nobody else is going to do it, we can.’ Livermore knows how to do lasers.”

So began a quest that would take the laser guide star from a theoretical concept to installation on the Keck Observatory in Hawaii, the largest ground-based telescope in the world at the time, in ten years. In this podcast, join Max and LLNL senior scientist Dee Pennington as they describe the challenges and successes involved in bringing the laser guide star to life. Listen on Apple or Spotify.