This plot shows the Transmission for 532 and 1064 nm as a function of the thickness of the SiO2 layer.
i.e. the thickness is constrained so that the optical thickness of the SiO2 and Ta2O5 pair is always 1/2 of a wavelength.
The top layer of the mirror is also fixed in this plot to be 1/2 wave.
This plot shows the result for 17 pairs. For 16 pairs, we are unable to get as low as 15 ppm for the 1064 nm transmission.