Experiment of the Month

Optics Lab; Laser Index of Refraction

Our new optic course, physics 331, is running for the first time this fall. We will examine several of the new laboratory exercises in that course. The picture below on the left shows four of our optics experimental stations.

Optics Lab Recraction

The first lab repeats an experiment from introductory physics, measuring the index of refraction of water. The purpose of the lab is to acquaint students with the Newport optical experimentation kits.

In the figure above, right, light travel from the helium neon laser is indicated by pink lines. Light is reflected from two mirrors arranged so that the final light path is angled downward into a container that is partly filled with water. A small piece of transparancy film lies across the top of the container in order to make the laser path visible (top round spot). A second piece of transparancy film is floated on the water to display the spot at which the light enters the water (middle round spot). When light strikes the bottom of the container, it is again visible (bottom round spot).

The round spots are placed at approximately the positions actually marked by the laser beam. The laser beam light itself did not reproduce well in these photos. From these spots, students can determine angle of incidence and angle of refraction, and verify Snell's law.

When Dr. Gilani had students add a little bit of black ink-jet printer ink to the water, two things happened:

  1. The ink scattered the laser light and made the light path through the water nicely visible.
  2. The index of refraction increased by about 10%