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Electric discharge generator for a nonchemical oxygen-iodine laser

Electric discharge generator for a nonchemical oxygen-iodine laser

In chemical oxygen-iodine lasers (COIL), the molecule of singlet oxygen (SO) O2(а1Dg) acts as an energy donor for radiating atomic iodine. However, the application of COIL is limited due to the necessity of using toxic substances to produce SO in a chemical generator. One of the alternative methods to generate SO is to produce it in an electric discharge. Generation in an electric discharge oxygen-iodine laser was first produced at the excitation of an oxygen-containing gas mixture and production of SO in a high-frequency (HF) discharge followed by mixing SO with iodine and cooling the laser mixture in the supersonic flow [D.L. Carroll et al., Appl. Phys. Lett. 86: 111104 (2005)]. Production of SO is performed in an electric-discharge SO generator. Then SO is transported to the zone of mixing with atoms of iodine, which is supplied by iodine-containing molecules. Radiation is generated at a wavelength of 1.316 μm immediately after the mixing of SO with atomic iodine in the laser cavity. The cooling of the gas mixture to cryogenic temperatures enables a positive amplification factor at a significantly smaller value of the SO yield, Y = [O2(a1Δg)]/[O2(X3∑g)] + [O2(a1Δg)], Ythresh ~1% at T = 100 K. For comparison, Ythresh ~ 15% at T = 300 K. A detailed review discussing the physics and techniques of producing SO in electric discharge, including in HF discharge, see in [A.A. Ionin et al., J. Phys. D: Appl. Phys. 40: R25 (2007)]. At present, the maximal power of an electric discharge COIL is ~500 W [D.L Carroll et al., Proc. SPIE 8677: 867702-1 (2013)]. The Defense Advanced Research Projects Agency (USA) supports a project  for the development of a 100-kW COIL with generation efficiency of ~10% [J. Hecht, Laser Focus World #9 41 (2011)].
Experimental studies of the output performance of an electric SO generator based on a pulsed electroionization discharge in oxygen-containing gas mixtures have demonstrated that addition of CO or H2 in an О2:Ar mixture of gases makes it possible to significantly increase the stability of electroionization discharge and to achieve a high value of the specific heat input (the maximal value in terms of molecular components of the mixture reached ~6.5 kJ·l–1·atm–1 (~150 kJ·mol–1) in a gas mixture of O2:Ar:CO = 1:1:0.1 at a full gas pressure of 30 Torr and an excitation volume of ~18 litres [A.A. Ionin et al., J. Phys. D: Appl. Phys. 36:982 (2003)]. It has been theoretically shown that, using mixtures with molecular additions of CO, H2 or D2, one can expect a yield of singlet oxygen О2(а1Δg) ~ 25%, exceeding its value required for the operation of the oxygen-iodine laser at room temperature [A.A. Ionin et al., J. Phys. D: Appl. Phys. 36:982 (2003)].
One of the promising discharges to produce SO and, respectively, to create an electric discharge oxygen-iodine laser is the slab-type capacitive HF discharge with transverse pumping of the gas mixture. The geometry corresponding to the transverse flow of gas with respect to sufficiently long electrodes makes it possible at relatively large gas pressures (several tens of Torr) to obtain SO concentrations at a level of ~10% and simultaneously to provide for diffusion cooling of gas without using a supersonic nozzle up to almost cryogenic temperatures. Besides, this geometry possesses a large transverse size of the gas flow (and, respectively, of the lasing zone), which makes it possible to avoid using laser mirrors with an extremely high reflection coefficient.
The kinetics of the slab HF discharge and its afterglow in oxygen-containing gas mixtures was experimentally and theoretically studied at the LGL. The major results of these studies were obtained at an experimental facility operating under static conditions, i.e., without a gas flow, which restricts the applicability of these results for creating and optimizing a real electric discharge system providing for both the efficient production of SO and its subsequent mixing with the flow of iodine. Recent works have experimentally and theoretically investigated an SO generator based on a slab HF discharge with the gas flow transverse with respect to relatively long electrodes. An experimental setup having no analogues was created, with the slab HF discharge and the subsonic gas flow, in which a possibility of precooling (before the discharge) the gas mixture and cooling the electrodes was provided for. This setup was used to investigate the effect of various experimental parameters for production of SO in the transverse HF discharge and its subsequent transportation to the assumed zone of mixing with iodine-containing gas components and further to the lasing zone.
The results of experiments and theoretical modelling give grounds to reckon on the lasing in an oxygen-iodine laser with the SO electric discharge generator based on the transverse HF discharge at the cooling of excited gas to temperatures of ~220 K, which is rather real even without using the supersonic expansion of the gas flow.

  1. A.A. Ionin, Yu.M. Klimachev, A.Yu. Kozlov, A.A. Kotkov, I.V. Kochetov, A.P. Napartovich, O.A. Rulev, L.V. Seleznev, D.V. Sinitsyn, N.P. Vagin, N.N. Yuryshev, Influence of nitrogen oxides NO and NO2 on singlet delta oxygen production in pulsed discharge. J.Phys. D: Appl. Phys., 42, 015201 (2009). http://iopscience.iop.org/0022-3727/42/1/015201/
  2. A.A. Ionin, Yu.M. Klimachev, O.A. Rulev, L.V. Seleznev, D.V. Sinitsyn, Transverse gas flow RF discharge generator of singlet delta oxygen for oxygen-iodine laser. 62-th Annual Gaseous Electronic Conference, October 20-23, 2009, Saratoga Springs, NY, USA. Bull.  Amer. Phys. Soc., 54, 12, 28 (2009).
  3. A.A. Ionin, Yu.M. Klimachev, I.V. Kochetov, A.P. Napartovich, O.V. Rulev, L.V. Seleznev, D.V. Sinitsyn, Slab HF discharge-based singlet oxygen generator with transverse gas flow for an electric-discharge oxygen-iodine laser. FIAN Preprint, No 14, 1–42 (2009). http://preprints.lebedev.ru/wp-content/uploads/2011/12/2009_14.pdf.
  4. А.А. Ionin, Yu. M. Klimachev, I. V. Kochetov, A. P. Napartovich, O. A. Rulev, L.V. Seleznev, D.V. Sinitsyn, Proc. SPIE, 7581, 758103 (2010).