The document describes an experiment using a Michelson interferometer to measure very small displacements on the order of the wavelength of light. It explains the basic principles of how the interferometer works using a laser, beam splitter, and two mirrors. It provides detailed instructions on assembling the experimental setup, aligning the optical components, taking measurements as air pressure is applied to introduce a displacement between the mirrors, and analyzing the results.

2. Optics experiment
Submitted by:
Muhammad Awais

4. Michelson Interferometer
 Background
 Interferometers generally are used to measure very small displacements by
using the wave property of light.
 If the wavelength is known one can use this principle to measure displacements
of the order of the wavelength of the light used.

5. Principle
 The principle of the Michelson interferometer is shown in Fig. Light from a laser is incident on a beam
splitter (BS) which consists of a glass plate with a partially reflective surface.
 About 50% of the light is reflected from the surface and 50% is transmitted.
 The reflected light (beam 1) hits mirror M1 and is reflected back towards the beam splitter.
 The transmitted light (beam 2) as well is reflected back towards the beam splitter by mirror M2. 50%
of the intensity of each reflected beam is transmitted/reflected towards the screen for observation.
 There the two beams overlap and constructive and destructive interference occurs depending on the
relative phase shift between the two plane waves.

6. FIGURE:

7. Experimental Equipment

8. Experimental Procedure
 When you are working with optical equipment NEVER touch the optical
surface with your fingers!
 If you have to tighten set screws use only two fingers and do not apply a lot of
force or you might crack a lens or a mirror.
 The various optical parts are labeled.
 If you are unsure ask your instructor or learning assistant for help

9. Assembling the Interferometer

10. CONTINUE…..
 Arrange the support parts as shown in Fig. 3. Note the various part are
labeled.
 Set the height of the laser to about 16.5 cm above the optical rail and make
sure all components are at the aligned at the same height.
 Turn the laser on. Adjust the output of the He-Ne laser parallel along the
optical rail (beam expander lens should not be inserted at this moment) by
carefully adjusting the set screws of the laser mount,
 Put in the beam splitter (BS) at an angle of 45^circ with respect to the beam
axis, and adjust its tilt to make the two beams (transmission and reflection)
parallel to table.

11. CONTINUE…..
 Adjust the tilt of mirrors M1 and M2 to make the reflected beams coincide
with their incident paths, and the two beam spots on the screen S overlap
together. Also make sure that the beam spots on the beam splitter overlap as
close as possible.
 Insert the beam expander lens, then finely adjust beam splitter, M1 and M2,
till concentric interference rings can be observed on the screen S Carefully
press on the optical table and observe how the fringes change. Interpret this
result. By how much does the difference |L_1 - L_2| change ?
 Insert the air chamber between beam splitter and M2 and adjust it parallel to
optical path. Mount the manometer as shown. Make sure you still see the
interference fringes

12. CONTINUE…
 At this point you might find that the system is very sensitive to vibrations. Ask
the instructor to let the optical table float. Once the table floats on air your
instrument should be much less sensitive to vibrations and be ready for
measurements. DO NOT LEAN ON THE TABLE WHEN IT IS FLOATING!
 Pump air into the air chamber till the maximum allowed pressure (40 kPa or
300 mm Hg) is reached and write it as Delta P
 Slowly release the air valve and count the number of interference rings
changing (appearing or disappearing) in the center till air pressure falls back
to zero.
 Repeat the previous two steps several times to obtain an average value and
an uncertainty.