Transmission Hologram With Reference Beam Experimenter: Chris Cleven This is a trial setup for a transmission hologram with a reference beam. The light strikes the object from two directions. We modeled after a procedure developed by Dan Wright. The holographic image below, with a die and a small plastic skull, was taken with an exposure time of about 40 seconds, whereas we had calculated 20 as the exposure which would give optimum density on the film. The viewing angle was quite narrow, and at a fairly extreme angle as illustrated.

A discussion with Clay Turner brought the following comments about the procedure:

• We should make the path lengths for the reference beam and the object beam equal within about 2-3cm. The above images had a pathlength difference of approximately 15 cm.
• There should be the same number of phase reversals in each beam, since the laser light has time-random elliptical polarization. This means the same number of mirrors in each beam - we had one mirror in reference beam. In the object beam, one part of it came from the sapphire lens and one part from the concave aluminum-foil mirror.