Concepts

Interference, diffraction

Overview

A laser beam is shone onto a variable rectangular aperture. The size of the hole determines the type of diffraction produces on the screen. Very small apertures produce Fraunhofer diffraction, and larger apertures produce Fresnel diffraction.

Details

Equipment

• [1] Variable rectangular aperture
• [1] Laser with beam expander
• [1] Optical rail
• [1] Slide mount
• [1] Saddle
• [2] Lab jack
  
• [1] Extension cord (if necessary) 

Classroom Assembly

1. Place the laser on top of the lab jacks, making sure the laser is pointed away from people.
2. Place the aperture on the optical rail.
3. Plug in the laser and aim it at the slit.
4. Adjust the size of the aperture such that the Fraunhofer diffraction pattern is visible.
5. Use the lab jacks to elevate the fringe pattern to a screen, if necessary.
6. Turn off the laser.

Important Notes

• Lasers can cause blindness. Use with caution.

Script

1. Turn on the laser.
2. Turn off the room light to see the diffraction pattern more easily.
3. Point out the Fraunhofer diffraction pattern.
4. Increase the aperture size by turning the two knobs of the variable aperture.
5. Point out the Fresnel diffraction pattern.
6. Turn off the laser.

Additional Resources