Toward a nonlinearity model for a heterodyne interferometer: not based on double-frequency mixing

Area of Science:

• Optical metrology
• Interferometry
• Precision measurement

Background:

• Picometer-level residual periodic errors in heterodyne interferometers challenge existing models.
• Current models based on double-frequency mixing fail to explain these observed errors.

Purpose of the Study:

• To propose a new theoretical model for analyzing residual periodic errors in heterodyne interferometers.
• To identify the underlying physical mechanism responsible for these errors.

Main Methods:

• Development of a new theoretical model incorporating multi-order Doppler frequency shift ghost beams.
• Construction of a novel experimental setup specifically designed to eliminate double-frequency mixing.
• Analysis of measurement signals from the novel setup.

Main Results:

• The new model successfully explains multi-order periodic errors.
• Multi-order Doppler frequency shift ghost beams from the measurement beam itself are identified as the cause.
• These errors occur independently of frequency mixing between incident beams.
• Experimental validation confirmed errors ranging from tens of picometers to one nanometer.

Conclusions:

• The phase mixing of the measurement beam itself is the source of multi-order periodic errors in heterodyne interferometers.
• The proposed model provides a more comprehensive understanding of error sources in high-precision interferometry.