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4.2. Reference Surface Generation
4.2 Reference Surface Generation
Reference surfaces record the optical aberrations in the system. The reference surface can be
subtracted from measurements to eliminate system aberrations, thus providing highly accurate
results. Reference files for PSI measurements are generated at the factory. If the system optics are
not changed, they should be satisfactory for all but the highest accuracy work. Reference surfaces
are rarely required for VSI measurements.
To generate a reference surface:
1. Place a clean super-smooth reference mirror on the stage.
Click the Measurement Options icon on the Measurement Setup ribbon to open the
Measurement Options Dialog.
2. Select the desired measurement type, either VSI or PSI (different references are required for
the different measurement modes).
3. Select the optics for which the reference surface is required.
4. Click the Generate button in the Measurement Parameters tab (see Figure 4.4).
Figure 4.4: Reference Surface Parameters
5. On the Reference Generation Setup dialog (see Figure 4.5), select:
Figure 4.5: Reference Surface Parameters
a) the number of locations to be measured.
• The effect of imperfections in the super-smooth reference mirror are minimized by
averaging multiple locations into the reference surface.
• Using multiple locations is more often necessary for higher magnification PSI mea-
surements, and generally four locations are sufficient even for the highest accuracy
work.
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