Laboratory Exercise 5
In this laboratory exercise students will build a simple interferometer.
They will split the output beam of a He-Ne laser into two beams which
will move along different paths, but eventually recombine. After
recombining, beams will produce an interference pattern on a screen.
Equipment:
1
3
1
4
He-Ne Laser
mirrors
beam splitter
post holders
Procedure:
In all optics experiments it is very important to align things properly
and to tighten things properly.
Turn on the laser.
Reflect the laser beam from the middle of mirror 1
approximately 50 cm away from the output hole back onto the
laser output hole. Use a mirror with a center-of-rotation adaptor
so you later can turn it easily, and use a collar to fix the height
of the mirror, so the height does not change when you loosen
the screw in the post holder to turn the mirror.
Use lens paper in the beam path to observe the incident as well
as the reflected beam and adjust the mirror so that the reflected
beam overlaps the incident beam.
Mount the beam splitter approximately 6 inches from mirror 1 at
a right angle to the laser - mirror 1 line, and mount each of the
other two mirrors without center-of-rotation adaptors
approximately 8 inches from the beam splitter as shown in the
figure below.
Rotate mirror 1 so that one of the laser beams strikes the center
of mirror 2, and then rotate the beam splitter so that the other
laser beam strikes the center of mirror 3.
Cover mirror 3 with an index card and adjust mirror 2, so that
the laser beam reflects from mirror 2 back onto the laser just
above the output hole. Use lens paper to help you view the
reflected beam.
Cover mirror 2 with an index card and adjust mirror 3, so that
the laser beam reflects from mirror 3 back onto the laser just
above the output hole.
Uncover both mirror and observe fringes on an index card.
Magnify the fringes using a lens.
Observe how the fringe pattern changes when you push lightly
against the post holder for one of the mirrors. Every relative
movement of 1/4 wavelength (1/4 *633 nm) will change a bright
fringe into a dark fringe and vice versa.
Insert a glass slide or a piece of plastic into one of the paths.
observe changes in the fringe pattern.
Laboratory 5 Report:
Name:
E-mail address:
In a few words, describe the experiment.
Comment on the procedure. Did you encounter difficulties or
surprises?
Describe your observations.