Z-Scan Fitting

I'm trying to fit z-scan data (two-photon absorption) using the equations below in Matlab but I'm unsure how to go about this. I measured T(z) and the ultimate goal is to elucidate beta.

I've tried cftool but the complexity of the system of equations has made it difficult

Answer 1

[Sanjay kannan M]

https://in.mathworks.com/matlabcentral/fileexchange/70114-open-aperture-z-scan-fit

Check this out.

You can obtain TPA co-efficient.

Feel free to give feedback.