alignment of the imaging unit:
put the surface reference and aling the IU in order to have the blade sharp image on the pd. Do a scan and move the z axis to the central peak maximum Maximize the AC/DC signalas goog as possible. Do again the scan (see first screenshot). The imaging unit position is 65.5mm, set exactly at the distance that have to be moved to measure the 154mm thick kagra sapphire. To measure the substrate we have to move the IU to 0mm.

Calibration: bulk reference
pump power=32mW, DC=4.1V, IUposition=65.5mm, AC=60mV (see second screenshot)

Maps of KAGRA substrate shinkosha#7: 130mm diameter, 1mm resolution, z_stage=110mm,70mm,35mm 

plot the maps with the same color scale