Nonlinear Errors Resulting from Ghost Reflection and Its Coupling with Optical Mixing in Heterodyne Laser...

Area of Science:

• Metrology
• Optical Engineering
• Physics

Background:

• Heterodyne laser interferometers are critical for high-precision measurements.
• Residual nonlinear errors limit achievable measurement accuracy, impeding picometer-level metrology.
• The source and mechanism of these residual errors remain poorly understood.

Purpose of the Study:

• To investigate the source and mechanism of residual nonlinear errors in heterodyne laser interferometers.
• To propose and experimentally verify a novel nonlinear model for these errors.
• To understand the impact of ghost reflections and optical mixing on interferometer performance.

Main Methods:

• Development of a novel nonlinear model incorporating optical mixing and ghost reflection.
• Experimental verification of the proposed nonlinear model.
• Analysis of nonlinear harmonics and their contribution to overall error.
• Investigation of the effect of ghost reflectance on the Heydemann correction.

Main Results:

• The study proposes a new nonlinear model involving optical mixing and ghost reflection.
• High-order and negative-order nonlinear harmonics from ghost reflection have negligible impact.
• Even small ghost reflections significantly degrade the Heydemann correction's effectiveness.
• Residual nonlinear error after correction is primarily determined by ghost reflectance.

Conclusions:

• Ghost reflection is the dominant factor in residual nonlinear errors after Heydemann correction.
• The effectiveness of the Heydemann correction is severely compromised by even minor ghost reflections.
• Understanding and mitigating ghost reflections is crucial for achieving picometer-level metrology.