Synthetic wavelength stabilization for two-color laser-diode interferometry

Area of Science:

• Metrology and Measurement Science
• Optical Physics and Engineering

Background:

• Conventional interferometers face phase ambiguity, limiting precise distance measurements.
• Two-color interferometry utilizes a synthetic wavelength from two laser frequencies to resolve phase ambiguity.
• High stability is critical for two-color interferometric laser gauges to ensure unambiguous fringe order determination over large distances.

Purpose of the Study:

• To derive upper limits on optical wavelength uncertainty for two-color interferometry.
• To express these limits as a function of optical path difference, phase errors, and synthetic wavelength.
• To propose and experimentally validate a simple stabilization system for long-term two-color interferometry.

Main Methods:

• Theoretical derivation of optical wavelength uncertainty limits.
• Development of a stabilization system using simultaneous servo control of two lasers with a single Fabry-Perot étalon.
• Experimental implementation and long-term testing of the stabilized two-color interferometric system.

Main Results:

• Established quantifiable upper limits for optical wavelength uncertainty.
• Demonstrated a simple, effective stabilization arrangement for two-color interferometry.
• Achieved 40 nm repeatability over 250 mm distance with a 15-mm synthetic wavelength over 16 hours; 8 nm repeatability for periods < 1000 s.

Conclusions:

• The proposed stabilization method effectively addresses the stringent stability requirements for two-color interferometric laser gauges.
• The system provides unambiguous fringe order determination over significant distances with high repeatability.
• This approach enhances the precision and reliability of optical metrology for large-scale applications.