Interference and Diffraction

1. Acquiring the Required Components for the Experiment

1. Obtain laser safety goggles and wear during this experiment before turning on the laser.
2. Obtain a piece of aluminum foil, and use scissors to cut it into two (approximately) 2 x 2 in square pieces.
3. Obtain two cardboards, each about 3 x 3 in, with a hole (diameter about 1 in) cut in the middle.
4. Obtain a device that can clamp the cardboard or a block to which the cardboard can be taped.
5. Obtain a few thin razor blades.
6. Obtain a He-Ne laser pointer with wavelength ~ 633 nm or green laser pointer with wavelength of 532 nm.

2. Single Slit Diffraction

1. Take an aluminum foil square and use a razor blade to cut a slit about 1 cm long in the middle of the foil. Use a ruler to help guide the razor to obtain a straight cut.
2. Tape the foil onto a cardboard square with the slit oriented horizontally inside the open hole (schematically shown in Figure 3a). Put tape around the corners of the foil (do not cover the slit). The cardboard helps to stabilize the foil during this experiment. Clamp one edge of the cardboard with the device (the cardboard should be perpendicular to the table surface), with the hole and horizontal slit exposed, and facing a white wall (which will be the screen) about 30 cm away.
3. Turn on the laser pointer and shine the laser beam (propagating in the direction normal to the foil) onto the slit. Observe the light pattern on the wall on the other side of the foil. Turn off the room light for better visibility of the pattern.

3. Double Slit Interference

1. Take the other aluminum foil. Stack 3 razor blades together but with the middle blade’s edge recessed from the other two blades’ edges. Use this stack to cut two closely-spaced slits in the middle of the foil (each about 1 cm long). Use a ruler to help guide the razor and make a straight cut.
2. Tape the foil onto the other cardboard (schematically shown in Figure 4a) and again support the cardboard with the vice or block, similar to step 2.2.
3. Turn on the laser pointer and shine the laser beam onto the double slit. Observe the light pattern on the wall on the other side of the foil. Turn off the room light for better visibility of the pattern.