Feedback-stabilized fractional fringe laser interferometer for plasma density measurements

Area of Science:

• Plasma physics
• Optical interferometry
• Laser diagnostics

Background:

• Accurate measurement of plasma electron densities is crucial for understanding plasma behavior.
• Traditional interferometry methods can be limited by environmental noise and slow drifts.
• Fractional fringe interferometry offers high resolution but requires robust stabilization.

Purpose of the Study:

• To develop and demonstrate a feedback stabilization technique for fractional fringe interferometry.
• To improve the sensitivity and stability of plasma electron density measurements.
• To address limitations caused by slow drifts and acoustic noise.

Main Methods:

• Utilized a CO2 laser Michelson interferometer with a pyroelectric detector.
• Implemented a feedback stabilization system employing an electromechanically translated mirror and a servo system.
• Employed a mechanical chopper to generate the servo control signal.

Main Results:

• Achieved a sensitivity of 3.4 x 10(-4) fringe on a 1-ms time scale.
• Demonstrated a sensitivity of 1.8 x 10(-2) fringe on a 10-ms time scale, despite acoustic pickup.
• The stabilization system exhibited a response time of 0.2 seconds and a measurement rise time of 45 microseconds.

Conclusions:

• The described feedback stabilization technique significantly enhances the performance of fractional fringe interferometers.
• This method enables precise measurement of plasma electron densities with improved sensitivity and stability.
• The technique is effective in mitigating slow drifts and reducing the impact of acoustic noise.