Based on design from Handbook of Coherent-Domain Optical Methods Needle Probes in Optical Coherence Tomography , Chapter 25.3.4 Optical Design of OCT Needle Probes, R. A. McLaughlin et al .
This code is for the case of a 3 GRIN probe with two optical windows.
The code calculates the q-factor after each element and plots the Gaussian beam waist through the system.
All lengths are microns. Distances must be integers.