# Homework Help: Laser Cavity Length

1. Mar 11, 2008

### Biest

Hi,

So I have a lab question for which I have to drive a formula to find the optical cavity length of a laser, $$L$$. I have results from testing the fringe patterns when I move one of the mirrors in a Michelson interferometer. It shows the typical $$\frac{\sin x}{x}$$ pattern. To find the cavity length, I use the distance between two high amplitude peaks, $$d$$, and the refractive index of the material inside the cavity, silicon in this case so 4.01. What I did was this, since the distance between peaks is the time between a wave has traveled $$2L$$, I figured that this formula has to be true:

$$\frac{2Ln}{c} = \frac{d}{c}$$

which will give me

$$2Ln = d$$

Is this accurate?

Thank you very much in advance.

Cheers,

Biest