Sometimes it may be important to simulate reflectivity during sample growth. This may be beneficial for controlling the growth of a sample in the MBE machine, and allows one to adjust growht parameters to match simulation (i.e. you may want to swich layer deposition at exact layers thicknesses, and this thickness may be obtained by comparing reflectivity from the sample with the results of a simulation - in short it can be really helpful). The picture below shows reflectivity evolution for three different wavelengths during growth of a sample with refractive indexes shown in the upper picture.

Simulation of reflectivity during sample growth.

You can find the python code and contribute on this project's page on Github.