Home > Events > PhD Candidate Brian W. Neiswander - "Electron Density Measurements for Plasma Adaptive Optics"

PhD Candidate Brian W. Neiswander - "Electron Density Measurements for Plasma Adaptive Optics"

Start: 4/10/2014 at 10:00AM
End: 4/10/2014 at 1:00PM
Location: 103 Multidisciplinary Research Building
Event Type:
  • Ph.D. Defense
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Over the past 40 years, there has been growing interest in both laser communications and directed energy weapons that operate from moving aircraft.  As a laser  beam propagates  from an aircraft  in flight,  it passes through  boundary layers, turbulence, and shear layers in the near-region of the aircraft. These fluid instabilities cause strong density gradients which adversely affect the transmission of laser energy to a target.  Adaptive optics provides corrective measures for this problem but current technology cannot respond quickly enough to be useful for high speed flight conditions. This research investigated the use of plasma  as a medium for adaptive optics for aero-optics applications.

When a laser beam passes through plasma, its phase is shifted proportionally to the electron density and gas heating within the plasma.  As a result, plasma can be utilized as a dynamically controllable optical medium.  Experiments were carried out using a cylindrical dielectric barrier discharge plasma chamber which generated a sub-atmospheric pressure, low-temperature plasma.  An electrostatic model of this design was developed and revealed an important design constraint relating to the geometry of the chamber.

Optical diagnostic  techniques were used to characterize the plasma discharge. Single-wavelength interferometric experiments were performed and demonstrated up to 1.5 microns of optical path difference  (OPD)  in a 633 nm laser  beam. Dual-wavelength interferometry was used to obtain time-resolved profiles of the plasma electron density and gas heating inside the plasma chamber. Furthermore, a new multi-wavelength infrared diagnostic technique was developed and proof- of-concept simulations were conducted to demonstrate the system’s capabilities.

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