# 4.2: In-lab Exercises

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## Holography: An Example of Diffraction

### 4.1 Viewing of Transmission, Reflection, White-Light and Computer-Generated Holograms

A collimated laser beam and a white-light source have been set up for viewing of four types of holograms.

1. Illuminate the given laser-made transmission holograms with the divergent laser beam (remove the large collimating lens). For each hologram, find the direction of propagation of the virtual image, and view it directly (i.e., no lens or screen is to be used to view this image). Move your head around and tilt the hologram to get the best view of the image. For the hologram of the clock or the hologram of the lion, draw a diagram of the setup that gives a virtual image with the best fidelity. In your diagram, show the location of the virtual image and any other beams that exit the hologram. Use this information to infer the geometry of the setup that was used to record the hologram (reverse engineering).
2. Illuminate the reflection hologram of the coins with the divergent laser beam and view the image through the hologram in reflection. Is the image you see real or virtual? Draw a diagram of the setup showing the location of the image and any other beams that exit the hologram. Use this information to infer the geometry of the setup used to record the hologram.
3. Illuminate the white-light hologram of the owl with white-light from the overhead lights in the Laboratory such that the light strikes the hologram and then reflects an image into your eye. Tip the hologram from side to side and up and down. Draw a diagram of your readout configuration showing the location of the image or images. Describe your observations from tipping the hologram in the beam. Re-illuminate the white light hologram with the divergent He-Ne laser beam. What differences do you observe? Explain these differences. Use your observations to infer the geometry of the setup used to record this hologram.
4. Put the collimating lens back into the system so as to generate a collimated laser beam. Illuminate the first computer-generated transmission hologram (written on a 4”x5” plate) with the collimated laser beam, and view the real image (it will spell a familiar acronym) on a distant screen. Draw a diagram of the setup showing the location of the real image and any other beams that exit the hologram. Use this information to infer the geometry of the setup used to record the hologram.
5. Place the second computer-generated hologram (written on 2”x2” film) into the collimated laser beam. Now relocate the screen close to second computer-generated hologram. Move the screen away from the hologram slowly. What do you observe on the screen? How do you explain what you see on the screen with respect to what you see on the actual hologram? Ask the TA or LA to show you how this hologram was made.