PASCO OS-8501 Interferometer User Manual

Page 16

scientific

Interferometer

012-02675B

M1 ALIGNMENT SCREWS

M1 ALIGNMENT BRACKET

BEAM SPLITTER

LENS HOLDER

DIFFUSER

THIN WIRE

OR THREAD

SPECTRAL LIGHT

SOURCE

MODEL OS-9287

LOW PRESSURE SODIUM

FIGURE 10 USING A SPECTRAL LIGHT SOURCE

Inteferometry with a Spectral Light Source

Although the Michelson Interferometer works best
with a laser light source, interferometry measurements
can be successfully made using any monochromatic
source of sufficient brightness. However, unless a
laser is used, it is generally not possible to project the
interference fringes onto a screen. The fringes are
viewed, instead, by looking into the beam-splitter.

A spectral light source such as the PASCO Model OS-
9287 Low Pressure Sodium Light Source works well
for this application. In addition to the spectral light
source, a diffuser is needed, such as PASCO Model

OS-9120.

To use the interferometer with a spectral or other
monochromatic light source:

➀

Tape two thin pieces of wire or thread to the sur-
face of the diffuser to form cross-hairs.

➁

Set up the equipment as shown below, and turn on
the light source. The light source should be on a
level with the interferometer mirrors.

➂

Adjust the alignment screws on the Fixed Mirror
(M

) until the front and back plates of the align-

ment bracket for M

are approximately parallel.

While looking through the beam-splitter toward
M

, adjust the rotation of the beam-splitter until

you see an image of the cross-hairs reflected from
M

➄

Now adjust the rotation of the Movable Mirror (M

)

until you see a second image of the cross-hairs.
Adjust the alignment screws on M

until the two

cross-hair images are superimposed. The interfer-
ence fringes should now be visible when looking
through the beam-splitter at M

➦

NOTE: If you are using a spectral light

source with spectral lines at several different
wavelengths, it may be necessary to use a filter
that blocks all but one of the spectral wave-

lengths.

➃