Polarization-modulated grating interferometer by conical diffraction.

Area of Science:

• Optics and Photonics
• Metrology
• Interferometry

Background:

• Grating interferometers in Littrow configuration use quarter wave plates (QWPs) for polarization modulation.
• Fabrication and mounting errors of QWPs introduce phase changes, leading to measurement errors in autocollimation optical path determination.

Purpose of the Study:

• To propose and evaluate an alternative grating interferometer design that bypasses errors associated with QWPs.
• To achieve high-precision displacement measurements with improved accuracy and repeatability.

Main Methods:

• A grating interferometer design producing conical diffraction was developed.
• The proposed system utilizes the grating itself for beam polarization modulation, replacing QWPs.
• Experimental validation was performed over a 45 mm range.

Main Results:

• The novel grating interferometer successfully bypassed errors originating from QWPs.
• A repeated measurement error of 40 nm was achieved over a 45 mm range.
• The system demonstrated a simple structure and good repeatability.

Conclusions:

• The proposed conical diffraction grating interferometer offers a robust alternative for high-precision displacement measurements.
• Eliminating QWPs significantly reduces a major source of error in grating interferometry.
• The system's simplicity and repeatability make it suitable for demanding metrology applications.