2/11/06clc

Microwave Optics

In this experiment you will demonstrate the wave nature of light in a number of interference, diffraction and reflection experiments using microwaves of ~ 3 cm wavelength.

The Sargent-Welch microwave transmitter Mark 2B emits microwaves at 10 mW/cm², which are well below standard limits for safety. However, good laboratory practice dictates that any exposure to microwaves should be kept to a minimum. Turn off the transmitter when you are not using it. If you wear an electronic pacemaker, inform the faculty person in charge of the laboratory before beginning the experiment.

Do all of the following:

A. Playing Around

Do experiments 1 and 2. Use the digital readout of power for all experiment. Do these experiments reasonably quickly: do not try to be precise.

Q. Which materials do not allow microwaves to be transmitted? Which do? Why? Try wood, metal and any other materials available. Verify that the microwaves are polarized.

Q. How does a polarizer work? Verify the law of reflection.

Do experiment 3 more carefully.

B. Standing Waves

Do experiment 4. Plot out the standing wave intensity.

Q. What is the wavelength of the microwaves as deduced from this experiment?

Q. Explain how standing waves occur. Write down an equation for the time and space dependence of the intensity.

C. Michelson Interferometer

Set up the apparatus in the Michelson interferometer configuration (expt. 5). In this experiment the emitted beam is divided into two parts by a beam splitter (half reflector) and then recombined to observe the interference between them. Determine the free space wavelength from the interferometer.

Q. When you mover either mirror, you will see maxima and minima. However, these might come from standing waves between receiver and mirror. How can you demonstrate that you are really operating an interferometer?

D. Diffraction

Do experiment 8.

Show that the angle at which the first minimum is given by a where a is the width of the slit. You have already determined lambda. Calculate the expected angles for the first minimum and first side maximum for single slit diffraction. Does it make sense?

Do experiment 9. Try to be reasonably precise and measure for both positive and negative angle. Make a nice graph, and compare your result to the theoretically expected one (see Halliday, Resnick and Walker for example).

E. Diffraction Gratings

Consider a beam of waves incident on a grating. Derive an equation relating the incidence and diffracted angles to S and . Determine by doing experiment 10.

Tips: Try to keep the source and detector as far from each other as possible. This experiment causes resonant cavities to occur everywhere. Before starting any diffraction measurements, adjust the detector distance for a maximum.