An important detail for the focus search is the Laser power. Usually the focus search is done with some overpower (for example at 200 RPM 5 Watts). Overpowering makes it fairly simple to check whether the smallest groves are in the center tracks.
This procedure for conventional imaging is absolutely sufficient. But whenever Micro Screens are imaged, this procedure does not show exactly the smallest tracks. Overpowering will create a set of equally wide Tracks and it is not possible to determine whether the truly smallest track is in the center of the tracks or more at one side.
For determining the exact focus offset, the following parameters should be used in the focus search.
Focus step 0.05 mm 200 RPM 1 Watt in general, the laser power should be equivalent to the power of one beam. For 38 advance beams and a laser power of 36 Watts this will result into: 0.947 Watts / Beam which is approximately 1 Watt. Set Axial Advance 0.05 and Focus Advance 0.05.
Best way to look at the focus search is with some light from top, thus the 3-dimensional structure of the cut marks in the LAMs layer can be seen most efficiently. This should be done with a microscope looking at the end of the focus search which is the closest to you while you are standing in front of the drum. Use a strong flash light and shine from the top of the drum toward the focus search.
Choose from the tracks which have the most sharply looking edges toward the center. By trend you should rather choose the higher track number than the lower one counting from the first track that was ablated left to right.
Use a strong small flashlight and good microscope.