Quasi-quadrature interferometer for plasma density radial profile measurements

Area of Science:

• Plasma physics
• Optical interferometry
• Instrumentation engineering

Background:

• Accurate measurement of time-dependent plasma properties is crucial.
• Traditional interferometers often require complex setups and multiple detectors.
• Existing methods can be sensitive to plasma-induced refractive and absorptive effects.

Purpose of the Study:

• To develop a novel Mach-Zehnder interferometer for precise measurement of fractional fringe shifts.
• To implement a quasi-quadrature technique for unambiguous density change detection.
• To reduce the size, cost, and complexity of plasma diagnostic instrumentation.

Main Methods:

• A continuous-wave (cw) Mach-Zehnder multichannel interferometer was designed.
• A quasi-quadrature technique was employed, time-multiplexing phase shifts in the reference beam.
• An electro-optic crystal for phase modulation was integrated into the common HeNe entrance beam using polarization techniques.

Main Results:

• Achieved measurement accuracy of one-fortieth fringe for time-dependent fractional fringe shifts.
• The quasi-quadrature method provides unambiguous density change information and automatic calibration.
• Fringe shift measurements demonstrated independence from plasma refractive and absorptive effects.
• The novel optical design significantly reduced crystal size, cost, and high-voltage requirements.

Conclusions:

• The developed interferometer offers a simplified and more robust method for plasma diagnostics.
• The quasi-quadrature design enhances measurement accuracy and reliability.
• This innovative approach minimizes equipment complexity and operational costs for plasma research.