Physics Department

	Physics Department
	Holography

The Physics Department of Goshen College has a new optical table for making holograms and other optical experimentation. In the photo, Josh Murphy (at left) and Craig Schmaus are setting up the table to make a holographic interferogram of a vibrating violin. Josh and Craig were at Goshen over the summer of '96 for this project as part of the Pew Science Program (currently the Maple Scholars Program).

The beam path starts with a 5mW He-Ne laser on the upper right of the picture. The beam passes through a beam splitter which reflects about 5% of it toward the beam spreader near the center of the table. This reference beam is reflected off an adjustable mirror at the top of the picture toward the film plate at the lower left. The rest of the beam passes through the splitter, off a mirror and through two lenses which spread it out to illuminate the entire violin. The reflected light from this object beam interferes with the reference beam to form the hologram pattern on the film.

Physics department

Goshen College

The developed film plate shows nothing but a strange patter of tiny fringes on it. To view the holographoc image, the film plate must be illuminated with the laser. When this is done the image at the left can be seen in true 3-D. Here we show a photograph of the illuminated hologram.

The Zebra-like pattern of fringes on the violin shows the modal pattern of vibration. The brightest stripe is the nodal line, this region is stationary. In the next bright stripe on either side the peak to peak amplitude of vibration is about 300 microns. The next line represents about 600 microns and so on in a sort of contour map of the vibration mode.

In the future we plan to compare this type of holographic image with a computer simulation method called Finite Element Analysis. Our aim is to better understand the vibrational modes of such objects.