Absolute calibration in grazing incidence interferometry via rotational averaging

Area of Science:

• Optical metrology
• Surface metrology
• Interferometry

Background:

• Interferometry at grazing incidence is suitable for testing cylindrical mantle surfaces.
• Systematic wavefront aberrations, particularly from diffractive beam splitters, limit the absolute accuracy of surface profiles.
• These aberrations stem from wavefront inversion within the interferometer setup.

Purpose of the Study:

• To investigate a calibration method to enhance the accuracy of surface profile measurements for cylindrical specimens using grazing incidence interferometry.
• To combine a four-position calibration technique with rotational averaging for improved metrology.
• To demonstrate the practical implementation and accuracy gains of this combined method.

Main Methods:

• Development and implementation of a four-position calibration method for grazing incidence interferometry.
• Integration of the rotational averaging procedure with the grazing incidence setup.
• Testing of hollow cylinder specimens using the enhanced interferometric technique.

Main Results:

• Successful implementation of the combined four-position calibration and rotational averaging method for grazing incidence.
• Measurement results for hollow cylinders demonstrating the effectiveness of the technique.
• Quantifiable gain in the absolute accuracy of the resulting surface profiles.

Conclusions:

• The investigated four-position calibration method, when combined with rotational averaging, effectively mitigates systematic wavefront aberrations in grazing incidence interferometry.
• This approach significantly enhances the accuracy of surface profile measurements for cylindrical optics.
• The presented method offers a robust solution for high-accuracy metrology of cylindrical surfaces.