Michelson's Interferometer; Standard Experiment; Experiment Setup; Performing Measurements - 3B SCIENTIFIC PHYSICS U10350 Manuel D'utilisation

The transmitting side is distinguished by a triangle
that is also shown on the sketched experiment set-
ups.
• Transport, storage: The eccentric arm
lie on the base of the finely adjustable mirror
on delivery so as to avoid any pressure points de-
veloping on the precision-turned eccentric
mechanism.
• Eccentric cleaning and maintenance: The turned
brass eccentric presses against a polished steel
sphere in the holder for the finely adjustable mir-
ror. Dust or other impurities can make the normally
smooth mirror adjustment uneven or "jerky". In this
case unscrew the eccentric base
are located on the underside of the base plate
and clean the brass eccentric as well as the steel
sphere. Use a soft rag soaked in petroleum ether,
acetone or something similar. When mounting the
eccentric make sure that there is a slight pressure
being exerted on the steel sphere. After assembly
is completed apply a drop of resin-free oil (sewing
machine or gun oil) to the contact point between
the eccentric and the steel sphere.
• Cleaning optical components made of glass: The
surface mirrors, the beam splitter, the diverging lens
and the windows of the vacuum cell can be cleaned
by carefully wiping them using a soft rag dipped in
ethanol (white spirit). Do not press too hard while
wiping! It is better to do the work using a lot of
ethanol and very little force. The glass plate on the
holder should only be wiped clean with a dry
bo
rag (if necessary just breathe on it), as otherwise
the adhesive foil strip (Twyman-Green experiment)
can come off.
5. Michelson Interferometer

5.1 Standard experiment

5.1.1 Experiment setup

•
The setup of the components on the base plate is
shown in Fig. 6. It is assumed in the following
description of the setup that all the basic settings
have to be made in advance.
•
Screw the He-Ne laser into its holder (see instruc-
tions for assembling laser) and place it so that it
is more or less straight in front of the diverging
lens.
•
Remove the adjustable mirror and beam splitter
and fasten the diverging lens straight on the base
plate.
•
Set the laser so that beam reflected back from the
finely adjustable mirror strikes the diverging lens
right in the center.
•
Loosen the knurled screw of the diverging lens
and pivot the lens out of the laser beam by approx.
90°.
•
Mount the adjustable mirror and adjust it with the
setting screws so that the distance between the
plate holding the mirror and the plate holding the
screws is just about even all round (5 - 6 mm).
should
9
as
7
(the screw heads
8
)
2
9
•
First loosely fit the beam splitter without tighten-
ing the screws so that its partially reflecting side
is in the direction of the angle scale, adjusting it
within narrow limits so that the two brightest
points visible on the observation screen are lo-
cated on or almost on a vertical line. Once this is
achieved the screws of the beam splitter are tight-
ened down.
•
Move the adjustable mirror with its adjusting
screws until the two brightest points on the screen
overlap each other precisely. This should already
lead to interference, which is noticeable because
of the flickering.
•
Turn the diverging lens back into the beam and
secure it in position so that the image is close to
the middle of the screen (i.e. the bright part of
the pattern should be centered not the interfer-
ence rings). Tilt the screen away from the vertical
enough so that the observer sees the brightest and
clearest image.
•
Now readjust the mirror again so that the inter-
ference rings are in the center of the screen.
Fig. 2: Experiment setup for the Michelson interferometer
•
In the setup the light propagation times are prac-
tically equal, leading to large, clearly discernible
distances between the interference rings. However
this also causes elliptical distortion of the rings
(even identical propagation times for the beams
at the mid point result in hyperbolic interference
patterns on the screen). In order to obtain near
circular rings the beam splitter can be rotated by
180°.

5.1.2 Performing measurements

•
Unscrew the micrometer screw counter clockwise
out to approx. 25 mm and then slowly screw it
back in clockwise to 20 mm. This avoids measure-
ment inaccuracies which may arise when the di-
rection of rotation is reversed.
•
Slowly turn the micrometer screw further in clock-
wise and at the same time count the number n of
rings produced. To judge whether a complete ring
has been produced, you can use the scale printed
on the observation screen. During the measure-
ments keep your breath away from the light beams
as much as possible because changes to air den-
sity are immediately discernible as "moving" in-
terference rings.
•
After at least 20 rings have been counted (the more
rings, the more accurate the measurement), read