Before starting with the calibration of the 3D system, the optic system needs to be well-calibrated in 2D. Then, the calibration of the 3D optic system (lookup table in SAMLight) is done with the following steps (see figure 85 for an overview):

1. Set up of the temporary lookup table
The lookup table is situated in Settings → System → Optic → Advanced → Correction, Settings → Z‑Correction, Settings (see figure 86).

Figure 86: Z-Correction Settings

•Set field size [mm]: Use the same value as in Settings → System → Optic → Lens → Size. (Set X gain to 1 and Y gain to 1).

•Set Distance mirrors [mm]: This value of the distance between the x and y mirror is given by the scan head manufacturer or can be estimated.

•Set Distance 2nd mirror to focus [mm]: This value defines the focus distance for SAMLight Z=0mm. This value has to be inside the Focus distance [mm] range of the Z lookup table (see figure 87). Please note that this distance is NOT the distance between the focus and the case of the scan head but between the focus and the position of the 2nd mirror inside the box of the scan head.

•Enable F-Theta lens if an F-Theta lens is used.

•Set up a temporary linear Z lookup table. Make sure, the value of Distance 2nd mirror to focus is within the lookup table. In the example given in figure 86 and below, the lookup table is set symmetrically around the Distance 2nd mirror to focus.

i.Example for typical Z shifting devices:

oDistance 2nd mirror to focus = 230mm

o-32767bit at  190mm

o0 bit at 230mm

o32767bit at 270mm

ii.Example for Optotune lens:

oDistance 2nd mirror to focus = 230mm

o20000bit at  190mm

o0 bit at 230mm

o-20000bit at 270mm

2. Preparation and marking of the test job:

 Figure 88: job file Calibrate_Optic3D_Circle_-120_to_120.sjf

a.Load the job file Calibrate_Optic3D_Circle_-120_to_120.sjf (see figure 89).

b.Remove unneeded Z values of the job:

i.Delete all Z values below Distance 2nd mirror to focus [mm] minus minimum of Z lookup table Focus distance [mm].
Example: 230mm - 270mm = -40mm. Delete entities from -120 to -42.

ii.Delete all Z values above 'Distance 2nd mirror to focus [mm]' minus 'maximum of Z lookup table Focus distance [mm]'.
Example: 230mm - 190mm = +40mm. Delete entities from +42 to +120.

iii.Save the reduced job with a new proper name.
Example: Calibrate_Optic3D_Circle_-40_to_40.sjf

c.Start marking at Distance 2nd mirror to focus [mm] (for Z =0) and optimize the marking:

i.Use a slow mark speed.
Example: Mark speed = 500mm/s

ii.Use a slow mark speed and a high jump delay.
Example: Jump delay = 3000µs

iii.Adjust the pen power (eventually use SAMLight Parameter Finder) that you can easily define the Best marked line in the marking result. Usually, you find the Best marked line at the middle of marked scale, see figure 90.

d.Mark the same job file at different Target heights which you reach for example with the mechanical z-axis (see figure 89 for illustration):

i.Decrease the distance between scan head and marking target step by step.

1.Mark the job on each Target height until you are completely out of focus (no more marking result).

2.Write next to each marking result the Target height.
Target height = Distance 2nd mirror to focus [mm] (for Z =0) minus distance between scan head and marking target
Note: Mind the sign! A distance between scan head and marking target smaller than Distance 2nd mirror to focus [mm] is related to a positive Target height (SAMLight Z value).

ii.Now increase the distance between scan head and marking target step by step (start marking at Distance 2nd mirror to focus [mm] (for Z =0)).

1.Mark the job on each Target height until you are completely out of focus (no more marking result).

2.Write next to each marking result the 'Target height'.
Target height = Distance 2nd mirror to focus [mm] (for Z =0)  minus distance between scan head and marking target
Note: Mind the sign! A distance between scan head and marking target greater than Distance 2nd mirror to focus [mm] can be related to a negative Target height depending on the Z-axis orientation in SAMLight.

Figure 92: Get the calibrated Z lookup table with the marking results from 2. and the excel file Calibrate_Optic3D_v0.9.3.xlsx

You can use the excel file Calibrate_Optic3D_v0.9.3.xlsx which you need to adjust according to your temporary lookup table and your measurement. Delete all lines that you did not use in your measurement.

a.Temporary linear lookup table: Insert the values of your temporary linear Z lookup table and Distance 2nd mirror to focus (Z = 0 focus dist) to the excel file (see figure 94)

b.Marking result from temporary lookup table: Insert the values of Scanner height and of the Best marked line for all valid marked target heights. The Best marked line must be read out from the marking result. The marking result consists of several lines corresponding to different z-values. Look for the line which is best in focus, meaning sharply marked and in the middle of the marked lines. Towards the edges, the lines should become less sharp and lighter. See figure 93 for illustration. Skip Best marked line values, which are very close to the limits of the Z range of the temporary linear lookup table.

c.Calibrated lookup table with linear and quadratic fit details. In the excel file, there is a graphic representation of the data. In this plot, you can check your data for inconsistencies like measurement errors. Decide if you want to use the linear fit or the quadratic fit.

It could be that your system does not need the full defined bit range from the temporary linear Z lookup table to reach the limit in z-range. Remember that you can only set points in the lookup table that are shifted maximum +/- FS/2 relative to the defined zero point in SAMLight. If you try to set the full calibrated linear/quadratic lookup table in SAMLight, you will get the error message telling that you are out of z limit.

Use the linear/quadratic fit function and use the theoretical focus distance limits from the temporary linear Z lookup table to calculate the bit value for the calibrated lookup table. Now you have the limits. If you use the quadratic fit, then remove all calculated points that are located outside your calculated limits.

Please note that the z-range is limited by the value of the field size (FS): starting with Z=0 (position of 'Distance 2nd mirror to focus [mm]', the reachable range is +/- FS/2.