Method to obtain a clear fringe pattern with a zone-plate interferometer

Area of Science:

• Optics and optical measurement
• Interferometry
• Metrology

Background:

• Zone-plate interferometers produce a bright central spot that obstructs interference fringe analysis.
• Existing methods like masking can lead to data loss, hindering complete fringe analysis.

Purpose of the Study:

• To propose a novel technique for efficient interference fringe analysis in zone-plate interferometry.
• To eliminate the central bright spot without compromising fringe data.

Main Methods:

• A zone plate with a specific phase fraction (π/2 or 3π/2) was employed.
• The technique is based on the principle of fringe-intensity reversal.
• The method was experimentally validated by measuring the shape error of a concave mirror.

Main Results:

• The proposed technique effectively diminishes the central bright spot.
• Complete fringe analysis was achieved, with no loss of fringe data.
• Experimental results for concave mirror shape error measurement showed good agreement with a Fizeau interferometer.

Conclusions:

• The fringe-intensity reversal technique offers an efficient and complete method for analyzing interference fringes in zone-plate interferometry.
• This approach overcomes the limitations of the central bright spot and data loss associated with other methods.
• The technique is suitable for precise optical metrology applications, such as shape error measurement.