Hänsch-Couillaud locking of a large Sagnac interferometer: advancing below the flicker floor

Area of Science:

• Geophysics
• Optical sensing
• Laser physics

Background:

• Active ring lasers are established rotation sensors in geosciences.
• Passive laser gyroscopes offer potential but require advanced stabilization techniques.
• Existing Pound-Drever-Hall stabilization is limited by residual amplitude modulation.

Purpose of the Study:

• To present the first Hänsch-Couillaud locked passive laser gyroscope.
• To address limitations of existing stabilization methods for passive laser gyroscopes.
• To achieve high sensitivity for geophysical rotation sensing.

Main Methods:

• Implementation of the Hänsch-Couillaud frequency stabilization technique for a passive laser gyroscope.
• Development of a cost-effective lock-in scheme to mitigate flicker noise.
• Characterization of the gyroscope's sensitivity and performance.

Main Results:

• The Hänsch-Couillaud method is limited by flicker noise.
• A novel lock-in scheme effectively overcomes flicker noise limitations.
• Achieved a sensitivity of 3.1 nrad/s, a fraction of 7.7×10^-5 of Earth's rotation rate.

Conclusions:

• The Hänsch-Couillaud locked passive laser gyroscope is a viable alternative for rotation sensing.
• The developed lock-in scheme enhances the performance of passive laser gyroscopes.
• This technology has significant implications for geodetic and seismological measurements.