Field emission excitation of a high pressure noble gas

Electric Hybrid Lasers (EHL) combines the benefits of a solid state laser (SSL) and a gas phase system. EHLs have the electrical capacity of an SSL and the thermal management and beam quality of a gaseous lasing medium. Researchers at Emory University have developed a novel EHL.1 A three-level EHL is being developed that utilizes a capacitively coupled RF discharge to produce metastable excited states of a Noble gas to and from the ground state of the laser. The lowest meta-stable state is optically pumped by employing diodes resonant with the highest energy state and then is spin mixed to transition to the lasing state. The atom then lases back to the beginning meta-stable state. To improve upon the efficiency of the capacitively coupled RF discharge for producing the meta-stable ground state, a new approach for producing meta-stables is investigated utilizing field emission into a high pressure Noble gas. If the electric field to pressure (E/P) ratio is kept sufficiently low, ions and electrons produced via ionization is negligible. The low E/P ratio is achieved due to the low turn-on electric field for the field emitters, thus the majority of the electrons in the gas are due to field emission, resulting in a highly non-neutral plasma. Experimental results have shown that individual field emission fibers can produce relatively high current of greater than a micro-Amp at extremely low electric fields (160 kV/m). In addition, experimental results show that at lower currents, the current-voltage characteristic is consistent with Fowler-Nordheim emission. At higher current levels, the current-voltage characteristic enters into a space charge limited regime where current increases as the square of the voltage. Excitation of the Argon gas using field emission was accomplished and spectroscopic measurements of the optical emission were made showing the lasing state was excited and relaxed to the ground meta-stable state. PIC simulations were able to reproduce the same trends observed in the experimental results. Experimental results showed that Argon meta-stables could be produced at E/P ratios well below what could be used to sustain a standard plasma discharge.