Design and implementation of a 120 GHz tracking interferometer with near diffraction limited focal spot

Area of Science:

• Plasma Physics
• Electromagnetics
• Optical Engineering

Background:

• Plasma opening switches (POS) are crucial for pulsed power applications.
• Accurate measurement of plasma density is essential for understanding POS behavior.
• Existing diagnostic methods may have limitations in resolution or complexity.

Purpose of the Study:

• To design and implement a 120 GHz monostatic tracking interferometer for measuring line-averaged plasma density in a POS source.
• To achieve a near diffraction-limited focal spot size suitable for the POS source dimensions.
• To develop a robust and noise-reduced system for operation in a pulsed power environment.

Main Methods:

• Utilizing a pyramidal horn and two cylindrical lenses for focusing quasi-optics to create a small focal spot.
• Employing a tracking receiver configuration to manage oscillator frequency drifts for heterodyne quadrature operation.
• Implementing battery power for all sources and amplifiers and other noise-reduction techniques to minimize system noise.

Main Results:

• Successfully designed and implemented a 120 GHz interferometer capable of producing a near diffraction-limited focal spot.
• The optical system effectively transforms an asymmetric Gaussian beam into a small focal spot.
• The tracking receiver configuration allows for stable operation without complex phase or frequency locking.

Conclusions:

• The developed 120 GHz interferometer is effective for measuring plasma density in POS sources.
• The optical design using cylindrical lenses provides a practical solution for achieving small focal spots.
• The noise-reduction techniques and tracking receiver enhance system performance in demanding environments.