The Objective of This Experiment Is to Find the Wavelength the Hene Gas Laser Using the Michelson Interferometer

Aim

The objective of this experiment is to find the wavelength the HeNe gas laser using the Michelson Interferometer.

Discussion

The relationship of λ, the wavelength of the laser, dm, the distance moved by the movable mirror(M2), and m, the number of fringes is given by the following formula:

λ=2dm/m

In this experiment, the focus lies on counting the number of fringes passing a reference point as the distance of M2 to the beam splitter is varied. As the number of fringes to be counted is large, there is a chance of miscounting the fringes. This error is reduced by varying the alignment screws of the fixed mirror M1 such that the fringes counted are thicker and spaced further apart. Another step taken to reduce this error is to adjust the focal lens to improve the clarity of the image of interference pattern formed on the screen. The reference mark is made on a fringe that is second from the center. The further away the fringe is from the center, the lower its clarity.

Even though the lab manual states that at the start of the experiment, the micrometer knob should be adjusted until the lever arm is parallel to the interferometer base, we decided to rotate the knob further, such that the lever is slightly pass the parallel position. The reason for this is that we will be counting up to 100 fringes which translates to a movement of the mirror by 31.65μm. One complete revolution of the mircometer knob is only 20μm. To maintain the linear relationship between the knob rotation and mirror movement even at large number of fringes, we decided to position the lever slightly pass the parallel position. However the disadvantage of doing so is that at the beginning portion of the experiment, when the lever is still displaced by a large amount, there is a tendency for the micrometer knob to continue to rotate