Chapter 9

Geometrical and waves optics

Michelson's rays

Take 15 minutes to prepare this exercise.

Then, if you lack ideas to begin, look at the given clue and start searching for the solution.

A detailed solution is then proposed to you.

If you have more questions, feel free to ask them on the forum.

A Michelson interferometer adjusted in blade air (thickness ) is illuminated by a point source of wavelength .

The output is placed a convergent lens of focal length and a screen in its image focal plane.

We reference on the screen bright rings whose radii are counted from the center :

Bright ring

1

2

3

4

5

5,02

7,11

8,7

10

12

Question

What is the path difference between two beams interfere in a point on the screen of a distance from the optical axis ?

Express as a function of , and .

Hint

Solution

The path difference is : (see the lesson about the Michelson interferometer)

Question

Deduce data the thickness of the air blade.

Hint

Solution

As , we deduce that :

and fringes can be exploited : given that the order of interference decreases as further away from the center :

We deduce as :

Question

What is the order of interference at the center ?

Hint

Solution

is order at the center. It was "almost" a bright fringe at the center.

Previous
The Michelson configuration "air blade" ("lame d'air", in french)
Next
Diffraction gratings