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Proceedings Paper

Latest developments toward the demonstration of a KW-class EOIL laser
Author(s): Alan E. Hill
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Paper Abstract

The electric oxygen iodine laser (EOIL) offers a vastly more practical, implementable, and safer alternative to its predecessor, the chemical oxygen iodine laser (COIL), particularly for airborne or other mobile military applications. Despite its promise and after 25 years effort, numerous laboratories around the world have not succeeded in providing the known basic physical requirements needed to electrically convert O2 into O2(a1Δ) with the fractional yields and efficiencies needed to make a practical laser. Hence, as of this date, the world record power generated from an EOIL device is only 6.5 watts. In this paper, a 30% conversion from O2 into O2(a1Δ) operating at substantial oxygen mass flow rates (0.090 moles O2/sec at 50 torr) and 40% electrical efficiency is reported. The O2(a1Δ) flow stream being produced carries 2400 watts. Gain measurements are currently in progress, to be followed shortly by power extraction. Current conditions imply that initial power extraction could push beyond 1 KW. Efforts to date have failed to generate substantial laser power because critical criteria have not been met. In order to achieve good O2(a1Δ) fractional yield, it is normally mandatory to impart on the order of 100 KJ/mole O2 while efficiently removing the waste heat energy from the generator so that less than a few hundred degrees Kelvin rise occurs due to gas heating. The generator must be excited by an electric field on the order of 10 Td. This is far below glow potential; hence, a fully externally sustained plasma generation technique is required. Ionization is supplied by means of applying short (tens of nanosecond) pulses to the O2(a1Δ) generator at 50,000 PPS, which are on the order of ten times breakdown potential. This enables a quasi-steady adjustable DC current to flow through the generator, being conducted by application of a DC, 10 to 14 Td pump E-field. This field is independently tunable. The result is that up to 180 KJ/mole O2 gets imparted to the gas by means of the 6 KW sub-breakdown pump field, while another 2700 watts is applied to the controlled avalanche field. The generator consists of 24 each, 1 cm diameter tubes that are submerged in rapidly circulating cold fluorinert. Heat is efficiently removed so that that the gas temperature, initially 273°K, raises only by 125°K, as evidenced by spectrographic analysis of the fine structure of O2(b1Σ) at lower pressure. Since all necessary conditions have been met, a 30% conversion rate of O2 to O2(a1Δ) has been achieved. Fortuitously, neither excited O atom production nor O2(b1Σ) production is visible in the spectra of the higher pressure, best yield runs. Essentially all other spectral lines are dwarfed in comparison the O2(a1Δ) line. Energy normally partitioned to O2(b1Σ) and apparently O atoms now feeds into O2(a1Δ) directly, enabling electrical efficiency to exceed 40%. As a continuation of this work, an I2 disassociating mixing section - then subsequently a 20 cm transverse M = 2.5 laser channel - has been coupled to the O2(a1Δ) generator. The effects of titrating NO, NO2, etc. to scavenge O atoms and O3 atoms is under current investigation. Laser power extraction will commence after having optimized all parameters to achieve maximum gain. Power extraction has been delayed due to substantial mechanical equipment failure; however, the apparatus has now been fully restored. Also, several modes of potential discharge instabilities peculiar to high O2(a1Δ) concentrations have been discovered. These phenomenon and their means of prevention will be discussed.

Paper Details

Date Published: 12 May 2008
PDF: 15 pages
Proc. SPIE 7005, High-Power Laser Ablation VII, 70051I (12 May 2008); doi: 10.1117/12.782656
Show Author Affiliations
Alan E. Hill, Texas A&M Univ. (United States)
Plasmatronics, Inc. (United States)


Published in SPIE Proceedings Vol. 7005:
High-Power Laser Ablation VII
Claude R. Phipps, Editor(s)

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