How Is the Value of 'm' Determined in Interference Equations?

[hyde2042]

Homework Statement

http://i.imgur.com/xrba7.png

Homework Equations

I'm using this equation to find the thickness of the polymer.

[(m+(1/2)) λ = 2nt] (where "n" is the index of refraction and "t" is the thickness )

The Attempt at a Solution

I just want to know how m is determined. I've learned everything else, but I missed the first day on which m value to use and it's always just slipped my mind whenever I'm in class or lab.

Thank you for your time.

 

[ehild]

m is any integer, including zero. ehild

 

[hyde2042]

Thanks, but I'm still unsure as to why "0" is used in the solution instead of "1" or "2".

 

[ehild]

Thanks, but I'm still unsure as to why "0" is used in the solution instead of "1" or "2".

First: it is easier to make a thinner coating then a thick one.

Second: The reflectance depends on the wavelength, this function is about the form R=A+Bcos(4piND/lambda) (N is the refractive index, D the thickness). If the reflectance is zero at a specific wavelength, it stays low in the broadest wavelength range when D has the smallest possible value.
The figure shows the reflectance spectrum of two coatings, one 100 nm, the other 300 nm thick. Both have zero reflectance at 600 nm.


ehild