Fracional-fringe holographic plasma interferometry

Area of Science:

• Plasma Physics
• Optical Metrology

Background:

• Holographic interferometry is a technique used for measuring phase shifts in transparent media.
• Standard holographic interferometry may face limitations in detecting very small phase shifts, particularly in low-density plasmas.
• Existing methods may be susceptible to apparatus motion, leading to spurious phase changes.

Purpose of the Study:

• To enhance the sensitivity of holographic interferometry for plasma density measurements.
• To adapt holographic interferometry for detecting plasma density shifts smaller than one fringe.
• To mitigate spurious phase changes caused by experimental setup movements.

Main Methods:

• Superposition of small fringe shifts from plasma density variations onto a background fringe pattern.
• Utilizing an arbitrarily shaped and positioned background fringe pattern.
• Leveraging the inherent advantages of holography, such as wavefront recording and reconstruction.

Main Results:

• Achieved increased sensitivity in holographic interferometry, comparable to conventional interferometry.
• Successfully applied the technique to plasmas with densities causing less than one fringe shift.
• Demonstrated simplified detection of spurious phase changes through the use of background fringes.

Conclusions:

• The proposed method significantly enhances the sensitivity of holographic interferometry for plasma diagnostics.
• This technique allows for the measurement of subtle plasma density variations previously undetectable.
• The background fringe method preserves the benefits of holography while improving robustness against apparatus instability.