Measuring Hair Thickness (Young slits)

[alonbab]

Homework Statement

Hi,

We're doing an experiment of measuring the thickness of a hair using a laser.
So we took a hair, and a laser, and shot it through the hair, to receive the following pattern on the wall.

The image of what we received (after red filter applied) on the wall is attached.We're confused though, about what we're seeing.

We would like, ideally, to measure the distance between two fringes, which will allow us to determine the distance of the slit (which is the thickness of the hair in our case).
However, we see that the central lighted area is larger than the secondary lighted areas. We thought this might be explained by the Beat pattern (sinc^2 cos^2), so the main lighted area would be the central "shell" caused by the sinc, and within it we get so many fringes that we cannot see them, we just see constantly lighted area.

Is this true? How can we measure the distance of the hair, given that image?

Homework Equations

The Attempt at a Solution

 

[TSny]

Hello alonbab. Welcome to PF!

According to http://en.wikipedia.org/wiki/Babinet's_principle]Babinet's[/PLAIN] principle the pattern from the hair should be the same as a http://tsgphysics.mit.edu/pics/Q%20Diffraction/Q2-Single-Slit-Diffraction.jpg

You can see that the width of the central max is greater than the width of the other maxima.