Bethel/Hamline Holography Collaboration

Some students at Hamline began studying the vibrational modes of a DVD in 2007. They mounted the disc on a mechanical vibrator and were then able to observe resonances. Resonances were made visible by pouring sand on the disc. The small grains would bounce off where the disc had large amplitudes and become trapped in the nodes.

They explored two means of mounting the disc. The first used a rubber washer and the second used two metal washers to clamp the disc in place. They saw some interesting behavior. Their set-up only allowed for experiments involving large amplitudes to capture the sand. They then contacted the Bethel physics department to discuss optical approaches.

This summer the two schools have been working together to collect data using real-time stroboscopic holography. First a hologram is created of a static DVD. Then the hologram is returned to its precise location and is brought into interference with the illuminated object. If the object is brought under some strain it flexes then fringes form from interference with the hologram. This allows for viewing of very small amplitudes of motion. By strobing the laser at approximately the frequency of the vibrator the motion can be recorded for video playback.

--Dave Swenson