Materials

HeNe Laser

Small Lab Jack

Green Diode Laser

Optics bench with Single Slit Set

Masking tape

Large Paper

Ring Stand with right angle and jaw clamp to hold the diode laser

Safety

The lasers we are using are just powerful enough that if you took a shot directly in the eye, you could damage your vision. Thus, we should take a few simple precautions to prevent the unlikely event of eye damage.

1. Never look directly into the laser beam. Laser light has a high intensity and can also be easily focused. A direct shot of the laser beam on your eye will be focused by your eye’s lens onto a small spot on your retina and can burn or possibly detach the retina.

2. Never hold an object by hand in front of the laser beam. This prevents the possibility of accidentally shining the light into your eyes.

3. Keep your head above the plane of the laser beam.

4. Whenever the light strikes an object, there will be a reflection. At times the reflections can be almost as strong as the incident beam. Know where the reflections are and block them if necessary.

5. If the laser has a shutter in front of the beam, use it. When not taking data, place the shutter in front of the laser beam. If there is no shutter then block the laser beam or turn off the laser when not using it.

Introduction

In this activity we will continue investigating the phenomena that make up the field of Physical Optics. Previously, we studied interference of light. In this activity we will investigate what happens to light when it passes through a small opening, This phenomena is known as diffraction.

Procedure and Questions

Use the small lab jack to position the HeNe laser at the end of the optical bench so that the laser beam is parallel to the tabletop and pointing towards a nearby wall. Place the Single slit set on the optics bench and position it in front of the laser so that the beam is normal to the slit labeled a = .16. This means the slidth has a width of .16 mm. Tape a piece of paper to the wall perpendicular to the pattern and trace the pattern of light produced on the paper.

Q1. In words, describe the pattern of light that is produced.

You should have observed alternating bright and dark spots. This pattern is called a diffraction pattern.

Q2. In what ways is the diffraction pattern similar to the interference pattern you observed in the previous activity?

Q3. In what ways is the diffraction pattern different?

D4. Mark the center of the location of the central bright spot and the bright spots to either side of the central bright spot.

Keeping the distance form the slit to the screen the same, rotate the single slit so that now the laser shines on the slit labeled .08. Adjust the paper so that the pattern for this slit lines up with the pattern from the previous slit.

D5. Mark the center of the location of the central bright spot and the bright spots to either side of the central bright spot.

Q6. When you changed to a narrower slit, what happened to the spacing of the spots?

Repeat the procedure above for the slit of witdth .04 mm and the slit of width .02 mm.

Q7. As the slit size gets smaller, what happens to the spacing of the bright spots in the patter?

Q8. What kind of relationship does there appear to be between the slit size and the spacing of the bright spots in the pattern?

Turn off the HeNe laser. Place the laser pointer in the jaw clamp so that the clamp will keep the laser on. Adjust the height and position of the diode laser so that it replaces the HeNe laser and hits the same slits as before. If not already there tape the paper back to the wall.

Once done, remove the laser from the clamp to turn it off.

D9. Mark the center of the location of the central bright spot and the bright spots to either side of the central bright spot.

Q10. How does the spacing between the bright spots change when the green laser shined on the slit instead of the red laser?

Q11. Which has a longer wavelength, the red or the green laser?

Q12. Does there seem to be a direct or inverse relationship between the wavelength and the spacing of the bright spots? Support your answer with evidence from your observations.

S13) Write a one paragraph summary of what you have learned about the pattern of light formed when a laser hits two closely spaced slits.