learning objective for yevon lee

1. Michelson Interferometer
In a Michelson Interferometer experiment, a light is split into two different
paths and reflected off mirrors before they combine again. It is important to
count the phase reversals (odd number) on the reflection and also since light
travels both directions, t is important to double the distance to get the correct
path length. In addition, adding a disturbance in a path alters the optical path
length and shifts the interference fringes. So, the change in optical path
length can be precisely measured by counting the # of fingers that shift
determines. The equation to find out when constructive interference occurs
is
A Michelson interferometer in use is operating at a wavelength of 400
nanometers and it has a 5 centimeter glass cell in the arm. Firstly, air is
puped out of the cell and a mirror is set up to make a bright spotin thee
centre of the intereference patten. Also, a valve is opened to slowly admit air
into the cell. The refraction index of the air at 1 atm pressureis 1.00045.
How many bright dark briht fringe shifts will be observed once the cell fills
with air?
1. First you must calculate the number of wavelengths in the glass tube
(.05/4.0e-7)= 125,000
2. Then you must calculate the wavelength of the light in the air
(4.0e-7/1.00045= 3.9982e-7
3. determine the length of the other arm
126,261=L2/(3.9982e-7)
L2 = .050481 meters

2. 4. calculate the number of wavelengths when the glass tube is filled
with air
(.05m)/(3.9982e-7)= 125,056
5. Calculate the number of shifts
2 x (125,056 – 125,000)= 112