Experiment 9: michelson interferometer, Experiment 10: fiber optics – PASCO WA-9316A Complete Microwave Optics System User Manual
Page 40
Experiment Guide
Teacher’s Guide
40
Experiment 9: Michelson Interferometer
Notes on the Procedure
1. through 4.
Best results are obtained when the mirrors are both a significant distance from the central beam-splitter. If either mirror is too
close to the center, the maxima splits into two peaks due to secondary interference effects.
From this it can be calculated that the wavelength is 2.80 cm
NOTE: An alternate method of analysis is to plot the reflector position versus fringe number. The slope of this line will be half
the wavelength.
By this method, the wavelength is calculated as 2.89 cm.
Answer to Question
1. The limit of resolution for distance measurements with a Michelson interferometer is roughly 1/4 the wavelength of the
light used. Thus with these microwaves, distance changes of about 7 mm can be measured. With a visible-light interfer-
ometer and a wavelength of 633 nm (HeNe laser light), distance changes of only 158 nm can be measured.
Experiment 10: Fiber Optics
Notes on the Procedure
2. The meter reading with the “optical fiber” bag in place can more than double the unobstructed meter reading. This is
because the bag prevents the normal spreading of the beam, and directs all the microwave radiation into the receiver horn.
3. The bag can direct the beam through a full 90° turn without measurable attenuation, if the curvature is gradual.
4. The signal begins to be attenuated with a radius of curvature of about 5 cm, and drops off rather suddenly from there. It is
difficult to get consistent results, though.
Answers to Questions
1. Theoretically one can use the radius at which the microwaves begin to “leak” to determine the index of refraction of the
material. In reality, this is quite difficult. Our values for n using this method range from 1.1 to 1.4.
n
Refl. Pos.
n
Refl. Pos.
1
75.0
12
90.9
1.5
2
76.4
1.4
13
92.3
1.4
3
77.9
1.5
14
93.8
1.5
4
79.4
1.5
15
95.2
1.4
5
80.8
1.4
16
96.6
1.4
6
82.2
1.4
17
98.1
1.5
7
83.7
1.5
18
99.5
1.4
8
85.1
1.4
19
101.0
1.5
9
86.6
1.5
20
102.4
1.4
10
88.0
1.4
21
104.0
1.6
11
89.4
1.4
Average
1.45