Add a probe to a laser module

I want to add a probe to a laser module to help with focusing.
I have ordered a capacitive sensor to give it a go.
I use GRBL 1.1h with config.h lines 129 and 155 modified for my machine.
I think that on the Uno board I can use A5 for the probe and if I can determine the material distance accurately from the laser module I should be able to set an offset for the Z position. I could then use some macros to reposition for various thicknesses of material that I would be cutting etc.
This is all in theory, so I wondered if anyone has some experience with this setup.