Professor Rai Weiss (MIT) talks with Robert Schofield (University of Oregon), while Bill Kells (Caltech) looks on. Live video images on the screen show to the scientists the laser light resonating in the two-kilometer long (~1.25 miles) optical cavities (upper left and upper right), recycled laser light incident on the beam splitter (lower left) and light reflected from the recycling mirror (lower right). The video images from the long optical cavities and the beam splitter are dark unless the interferometer becomes locked on resonance.