Picometer level displacement metrology with digitally enhanced heterodyne interferometry

Area of Science:

• Laser metrology
• Optical physics
• Gravitational wave detection

Background:

• Digitally enhanced heterodyne interferometry (DEHI) is an emerging laser metrology technique.
• It utilizes pseudo-random codes phase-modulated onto an optical carrier for precise measurements.
• Characterizing its displacement sensitivity is crucial for its application.

Purpose of the Study:

• To present the first characterization of DEHI's displacement sensitivity.
• To compare DEHI's performance against a conventional measurement technique.
• To assess DEHI's suitability for advanced gravitational wave detector applications.

Main Methods:

• Displacement of an optical cavity was measured using DEHI.
• Measurements were simultaneously compared to conventional Pound-Drever-Hall locking.
• A real-time signal extraction system on a field-programmable gate array (FPGA) was employed.

Main Results:

• DEHI displacement measurements agreed with Pound-Drever-Hall locking to within 5 pm/√Hz at 1 Hz.
• This agreement provides an upper bound for DEHI's displacement noise.
• The FPGA-based system demonstrated suitability for real-time control.

Conclusions:

• DEHI exhibits high displacement sensitivity, comparable to established methods.
• The technique is a viable option for lock acquisition in advanced gravitational wave detectors.
• Real-time signal processing on FPGAs enables practical implementation of DEHI.