[R] how to fit gauss beam?

[Thomas Hunger]

Reply to self:
> I am having a hard time fitting a gauss beam using R. In
> gnutplot I did something like
>
> $ w(z) = w0 * sqrt(1+(z/z0)**2)
> $ fit w(z) 'before_eom.txt' using 1:2 via w0, z0
>
> to obtain w0 and z0. Now I want to do the same in R. I
> tried a linear model like this (r = radius, z =

This works fine:

data <- read.table ("nach_eom.tab", header=T)

M <- 1.1
nls (major ~ M*w0*sqrt(1+(d/z0)^2), 
     data = data, 
     start = list(w0 = 460, z0=0.02))