CO2 laser-based dispersion interferometer utilizing orientation-patterned gallium arsenide for plasma density...

Area of Science:

• Plasma Physics
• Nonlinear Optics
• Laser Interferometry

Background:

• Accurate measurement of electron density is crucial for understanding plasma behavior.
• Traditional interferometry methods can face limitations in sensitivity and spatial resolution.
• Nonlinear optical techniques offer potential for enhanced diagnostic capabilities.

Purpose of the Study:

• To develop and demonstrate a novel dispersion interferometer for plasma electron density measurement.
• To utilize second-harmonic generation in orientation-patterned gallium arsenide for enhanced sensitivity.
• To assess the performance of the interferometer in a pulsed radio-frequency argon plasma.

Main Methods:

• A dispersion interferometer was constructed using a carbon dioxide laser and orientation-patterned gallium arsenide nonlinear crystals.
• The interferometer employed two nonlinear optical crystals positioned on opposite sides of the plasma.
• Electron line densities were measured using a phase-extraction technique combining successive plasma pulses.

Main Results:

• The developed interferometer successfully measured electron line densities in a pulsed radio-frequency argon plasma.
• A noise-equivalent line density of 1.7 × 10^17 m⁻² was achieved within a 950 kHz detection bandwidth.
• Individual and sequential nonlinear crystals demonstrated efficient second-harmonic generation, producing up to 58 mW of peak power.

Conclusions:

• The dispersion interferometer based on second-harmonic generation is a viable tool for plasma electron density diagnostics.
• The instrument demonstrates good sensitivity and performance in measuring electron line densities.
• The use of orientation-patterned gallium arsenide shows promise for efficient nonlinear frequency conversion in plasma diagnostics.