Fringe-counting technique used to lock a suspended interferometer

Area of Science:

• Optics and Photonics
• Gravitational Wave Detection
• Precision Measurement

Background:

• Michelson interferometers are crucial for detecting minute displacements.
• Controlling mirror alignment is essential for sensitive measurements, especially in gravitational wave detectors.
• Existing methods for large displacement measurement can be complex or require additional optical components.

Purpose of the Study:

• To implement a novel digital fringe-counting technique for real-time measurement of relative mirror displacement.
• To provide an effective error signal for servo mechanisms to reduce displacement.
• To offer a simplified locking procedure for interferometric gravitational wave detectors.

Main Methods:

• Utilizing a digital fringe-counting technique on a suspended Michelson interferometer.
• Employing modulated optical path length for oscillations significantly larger than the laser wavelength.
• Developing a servo mechanism driven by the error signal from the fringe-counting technique.

Main Results:

• Real-time measurement of relative mirror displacement was achieved.
• The technique successfully generated an error signal to reduce displacement within half the laser wavelength (λ/2).
• The method requires no additional optics or polarizers.

Conclusions:

• The digital fringe-counting technique offers a robust and simplified method for measuring and controlling large mirror displacements.
• This technique is directly applicable as a starting procedure for locking systems in interferometric gravitational wave detectors.
• The absence of extra optical components makes the technique practical and cost-effective for sensitive interferometry.