A team of researchers at Lawrence Livermore National Laboratory in Livermore, Calif., has determined that Shack-Hartmann wavefront sensors offer sufficient sensitivity to replace phase-shifting interferometers for the characterization of large optics. Both instruments are commercially available, but interferometers are more expensive and are prone to problems with vibration in the test environment. The researchers, who reported their findings in the Sept. 1 issue of Applied Optics, compared the sensors' performance in a lab designed to characterize deformable mirrors for the National Ignition Facility. An instrument from Wavefront Sciences Inc. of Albuquerque, N.M., represented commercially available Shack-Hartmann sensors. Both simultaneously measured the surface of a 400-mm-sq mirror and displayed a systemic difference of less than 20 nm rms in their measurements.