Closed-loop phase-shifting interferometry with a laser diode

Area of Science:

• Optical Engineering
• Metrology
• Interferometry

Background:

• Fizeau-type interferometers are crucial for high-precision optical surface measurements.
• Traditional interferometers face challenges with environmental disturbances and laser stability.
• Phase-shifting techniques enhance measurement accuracy but require stable control.

Purpose of the Study:

• To construct a closed-loop phase-shifting Fizeau interferometer.
• To implement direct frequency modulation of laser diodes for phase control.
• To achieve stable and precise optical phase measurements.

Main Methods:

• Utilized a Fizeau-type interferometer configuration.
• Employed direct frequency modulation of laser diodes at lambda=633 nm.
• Implemented a servo control system in the phase domain.
• Used a two-frequency optical heterodyne method for optical phase detection.
• Achieved stepwise phase shifting.

Main Results:

• Successfully constructed a closed-loop phase-shifting Fizeau interferometer.
• Demonstrated servo control in the phase domain for stable optical phase detection.
• Achieved good stabilization against vibrations, airflow, and laser frequency fluctuations.
• Validated the effectiveness of direct frequency modulation for phase control.

Conclusions:

• The developed interferometer provides a stable and precise platform for optical metrology.
• Direct frequency modulation of laser diodes is an effective method for closed-loop phase control in interferometry.
• The system shows robustness against common environmental and laser instabilities.