Here is the code I've been working on for mode matching to the cavity. MM.m is adapted from goo2.m from Rana's page (http://www.ligo.caltech.edu/~rana/mat/MM/PMCmatch/), and there you can also find the functions called by MM.m that I didn't edit, such as chaindo. It finds the optimum focal lengths and distances for the lenses.

EtaCalcSimple calculates the overlap function for the beam assuming a non-astigmatic beam and an astigmatic cavity. 

MMplot plots the values for z (distance from the waist) and w as a function of the changing distance from the mirror to the first lens.

Calculate allows you to change values such as the distances to see how this affects the values for eta, the waist size, and z.

***EDIT  Alastair Heptonstall ***

I've taken all of the .m files and put them in an archive file.