Light Used to Measure Surface Vibrations

A technique that passively monitors light intensity modulation is able to measure the physical and optical properties of a vibrating surface.

A team from the University of Louisville, in conjunction with Spectral Sciences Inc. and the U.S. Air Force Research Laboratory, used high dynamic range cameras with large focal planes to detect tiny changes in the surface normal of various objects.

The technique can be used to produce an image of the changing normal without touching the surface or altering its state, the researchers said. It also can image any object to determine its vibrational properties with or without active illumination.

Fractional modulation of a pneumatic membrane forced into the (0,1) mode by inflating (left) and deflating (right) the membrane, relative to neutral pressure. Courtesy of SPIE.

When a surface vibrates, an infinitesimal unit area that is presented to the illumination source changes its orientation. The researchers found the surface normal of that unit area deflects slightly, which results in a small modulated component in scattered light.

The small temporal modulation that is present in scattered light was found to extract vibrational properties of any surface. The researchers said this allowed them to change the distance to the subject or use a zoom lens to examine any arbitrary surface area — the entire object or a small portion of it.

The researchers added that because surface vibrations can be imaged at any scale, the technique can also work with microscopes and fish-eye lenses.

The work was funded by the U.S. Air Force Office of Scientific Research. The research was published online by SPIE Newsroom (doi: 10.1117/2.1201407.005544).