Precision Interferometer
012-07137A
12
6.
Record
d
m
, the distance that the movable mirror moved toward the beam-splitter according to your
readings of the micrometer knob. Remember, each small division on the micrometer knob corre-
sponds to one µm (10
-
6
meters) of mirror movement.
7.
Record
N,
the number of fringe transitions that you counted.
8.
Repeat steps 3 through 7 several times, recording your results each time.
9.
Go on to part two. If you have time afterward, try setting up the interferometer in Fabry-Perot mode
and repeating steps 3 through 8.
Part II : Polarization (using the Calibrated Polarizer, part of OS-9256A Interferometer Accessories)
1.
Place a polarizer between the laser and the beam-splitter. Try several polarization angles. How does
this effect the brightness and clarity of the fringe pattern?
2.
Remove that polarizer and place a polarizer in front of the fixed or movable mirror. Try several
polarization angles. How does this effect the fringe pattern?
3.
Now try two polarizers, one in front of the fixed mirror, and one in front of the movable mirror. First
rotate one polarizer, then the other. Again, note the effects.
Analysis
Part I
1.
For each trial, calculate the wavelength of the light (
l
= 2
d
m
/
N
), then average your results. If you tried
the Fabry-Perot mode also, calculate the wavelength independently for that data. The same formula
applies.
Part II
1.
From your observations in step 1 of the procedure, can you determine the polarization characteristics
of your light source? Does it vary with time?
2.
Do your observations from step 2 give you any more information about the polarization of your
source?
3.
From your observations in step 3, do cross-polarized beams interfere?
Questions
1. I
n the calculation to determine the value of
l
based on the micrometer movement, why was
d
m
multiplied by two?
2.
Why move the mirror through many fringe transitions instead of just one? Why take several measure-
ments and average the results?
3.
If you tried the Fabry-Perot mode, was your measured
l
the same? If not, can you speculate about possible
reasons for the difference? Do you have more confidence in one value as opposed to the other?
4.
If the wavelength of your light source is accurately known, compare your results with the known
value. If there is a difference, to what do you attribute it?
5.
When measuring mirror movement using the micrometer dial on the interferometer, what factors limit
the accuracy of your measurement?
6.
When measuring mirror movement by counting fringes using a light source of known wavelength,
what factors might limit the accuracy of your measurement?
7.
What role does polarization play in producing an interference pattern?
