Suppression of air refractive index variations in high-resolution interferometry

Area of Science:

• Metrology and Measurement Science
• Optical Physics
• Materials Science

Background:

• Interferometric displacement measurements are limited by air's refractive index fluctuations.
• Existing methods struggle to accurately account for environmental variations.
• High-precision measurements require compensation for refractive index errors.

Purpose of the Study:

• To develop a new technique for reducing uncertainty in interferometric displacement measurements.
• To eliminate errors caused by the differing positions of interferometer laser beams and air sensors.
• To combine length measurement with real-time refractive index monitoring.

Main Methods:

• Utilized two counter-measuring interferometers: one for displacement and one as a tracking refractometer.
• Referenced the laser source wavelength to a mechanical standard with ultra-low thermal expansion.
• Integrated length measurement with in-axis refractive index fluctuation measurement.

Main Results:

• The proposed technique successfully combines displacement and refractive index measurements.
• Errors due to sensor and beam positioning differences were eliminated.
• Achieved an agreement of 5 × 10⁻⁸ over a 1 K temperature range in experimental tests.

Conclusions:

• The dual-interferometer approach effectively mitigates refractive index influence on displacement measurements.
• This method enhances accuracy by compensating for environmental variations in real-time.
• The technique offers a significant improvement for high-precision metrology applications.