Digitally controlled laser frequency stabilization for a ring laser using saturated absorption

Area of Science:

• Atomic, Molecular, and Optical Physics
• Laser Physics and Technology
• Control Systems Engineering

Background:

• Precise control of continuous wave (CW) laser frequency is essential for advanced scientific applications, particularly in cold atom studies.
• Traditional laser locking techniques often require frequency dithering, which can complicate experiments and limit stability.
• Existing methods for laser frequency stabilization may not offer the required precision or adaptability for diverse experimental needs.

Purpose of the Study:

• To develop and demonstrate a digital system for highly stable frequency control of a CW ring laser.
• To implement a feedback mechanism utilizing Doppler-free absorption and the Zeeman effect without requiring laser dithering.
• To assess the performance and stability of the developed digital laser locking system.

Main Methods:

• A digital control system was designed, integrating a vapor cell for Doppler-free absorption and a time-varying magnetic field exploiting the Zeeman effect.
• Active feedback was implemented using a microcontroller to process digitized signals from the vapor cell and magnetic field.
• A bias magnetic field was incorporated to enable frequency tuning over several MHz while maintaining lock.

Main Results:

• The digital system successfully locked the CW ring laser frequency to a resonance peak with standard deviations ranging from 250 to 450 kHz over 1 hour.
• The system achieved excellent frequency stability, with Allan deviations reaching 6 × 10^-11 at a 10-second averaging period.
• Measurements confirmed the system's ability to maintain stable laser frequency and showed good agreement with a commercial wavemeter.

Conclusions:

• The developed digital laser frequency control system provides a robust and stable solution for demanding scientific experiments.
• The system's design, leveraging Doppler-free absorption and Zeeman-tuned feedback, eliminates the need for laser dithering, enhancing stability.
• This adaptable digital control system has broad applications in cold atom physics, wavemeter calibration, and controlling various CW laser systems for different atomic targets.