Noble gas meta-stable state excitation using carbon nanotube fiber cathodes

Summary form only given. Electric Hybrid Lasers (EHL) are of great interest for commercial and government application due to their ability to combine the benefits of a solid state laser (SSL) with the benefits of a gas phase system. EHLs have the electrical capacity of an SSL and the thermal management and beam quality of a gaseous lasing medium. Recently, researchers at Emory University have developed a novel EHL.¹ The Discharge Assisted Noble Gas Laser (DANGL), is a three-level laser that utilizes a mild electrical discharge to produce metastable excited states of a Noble to form the ground state of the laser. The meta-stables are optically pumped by employing diodes resonant with the highest energy state. After excitation, relaxation via collisions with helium from the highest excited state to the lasing state occurs. The atom then lases back to the metastable state. To improve upon the efficiency of the mild electrical discharge of the original DANGL, a new approach for producing meta-stables is investigated utilizing field emission from Carbon-Nanotube (CNT) fibers into a high pressure Noble gas. If the electric field to pressure (E/P) ratio is kept sufficiently low and pulse widths are short, ionization is significantly reduced. Not allowing for full sustained breakdown allows the majority of the electrons in the gas to result from field emission from the CNT fiber, thus creating a non-neutral plasma. Modeling of the DANGL meta-stable excitation was accomplished with a combined 3-D electromagnetic Particle-in-Cell (PIC) and Monte Carlo Collision (MCC) model. Modeling was performed to optimize the geometry of field emission from the CNT fibers in order to maximize the yield of meta-stable states. Model results showed high yields of Ar meta-stables could be achieved at E/P ratios that could not sustain a standard plasma discharge. Model results enabled the development of optimized experimental set-up and interpretation of the experimental current-vol- age characteristics. Experimental results have also shown that CNT fibers can produce relatively high current pulses for extremely low electric field (160 kV/m) at a 5 nanosecond pulse width, thus enabling Noble gas meta-stable excitation without neutral plasma production.