The chemistry of electric discharge driven oxygen iodine lasers (EOIL) has long been believed to have O2(a1▵g) as the
sole energy carrier for excitation of the lasing state I(2P1/2), and O(3P) as the primary quencher of this state. In many sets
of experimental measurements over a wide range of conditions, we have observed persistent evidence to the contrary. In
this paper, we review our experimental data base in both room-temperature discharge-flow measurements and EOIL
reactor results, in comparison to model predictions and kinetics analysis, to identify the missing production and loss
terms in the EOIL reaction mechanism. The analysis points to a significantly higher level of understanding of this
energetic chemical system, which can support advanced concepts in power scaling investigations.
Scaling of Electric Oxygen-Iodine Laser (EOIL) systems to higher powers requires extension of electric discharge
powers into the kW range and beyond, with high efficiency and singlet oxygen yield. This paper describes the
implementation of a moderate-power (1 to 5 kW) microwave discharge at 30 to 70 Torr pressure in a supersonic
flow reactor designed for systematic investigations of the scaling of gain and lasing with power and flow conditions.
The 2450 MHz microwave discharge is confined near the flow axis by a swirl flow. The discharge effluent,
containing active species including O2(a1▵), O(3P), and O3, passes through a 2-D flow duct equipped with a
supersonic nozzle and cavity. I2 is injected upstream of the supersonic nozzle. The apparatus is water-cooled, and is
modular to permit a variety of inlet, nozzle, and optical configurations. A comprehensive suite of optical emission
and absorption diagnostics monitors the absolute concentrations of O2(a), O(3P), O3, I2, I(2P3/2), I(2P1/2), small-signal
gain, and temperature in both the subsonic and supersonic flow streams. The experimental results include numerous
observations of positive gain and lasing in supersonic flow, and the scaling of gain with a variety of flow and
reaction rate conditions. The results are compared with kinetics modeling predictions to highlight key discrepancies
as well as areas of agreement. The observed gains are generally lower than the predicted values, due in part to
chemical kinetics effects and also due to mixing limitations specific to the reagent injection design. We discuss in
detail the observed effects related to O-atom chemistry, and their import for scaling the gain to higher levels. We
also will present initial beam quality measurements.
Scaling of EOIL systems to higher powers requires extension of electric discharge powers into the kW range and
beyond with high efficiency and singlet oxygen yield. We have previously demonstrated a high-power microwave
discharge approach capable of generating singlet oxygen yields of ~25% at ~50 torr pressure and 1 kW power. This
paper describes the implementation of this method in a supersonic flow reactor designed for systematic investigations of
the scaling of gain and lasing with power and flow conditions. The 2450 MHz microwave discharge, 1 to 5 kW, is
confined near the flow axis by a swirl flow. The discharge effluent, containing active species including O2(a1Δg, b1Σg+),
O(3P), and O3, passes through a 2-D flow duct equipped with a supersonic nozzle and cavity. I2 is injected upstream of
the supersonic nozzle. The apparatus is water-cooled, and is modular to permit a variety of inlet, nozzle, and optical
configurations. A comprehensive suite of optical emission and absorption diagnostics is used to monitor the absolute
concentrations of O2(a), O2(b), O(3P), O3, I2, I(2P3/2), I(2P1/2), small-signal gain, and temperature in both the subsonic and
supersonic flow streams. We discuss initial measurements of singlet oxygen and I* excitation kinetics at 1 kW power.
Generation of singlet oxygen metastables, O2(a1Δ), in an electric discharge plasma offers the potential for development of compact electric oxygen-iodine laser (EOIL) systems using a recyclable, all-gas-phase medium. The primary technical challenge for this concept is to develop a high-power, scalable electric discharge configuration that can produce high yields and flow rates of O2(a) to support I(2P1/2->2P3/2) lasing at high output power. This paper discusses the chemical kinetics of the generation of O2(a) and the excitation of I(2P1/2) in discharge-flow reactors using microwave discharges at low power, 40-120 W, and moderate power, 1-2 kW. The relatively high E/N of the microwave discharge, coupled with the dilution of O2 with Ar and/or He, leads to increased O2(a) production rates, resulting in O2(a) yields in the range 20-40%. At elevated power, the optimum O2(a) yield occurs at higher total flow rates, resulting in O2(a) flow rates as large as 1 mmole/s (~100 W of O2(a) in the flow) for 1 kW discharge power. We perform the reacting flow measurements using a comprehensive suite of optical emission and absorption diagnostics to monitor the absolute concentrations of O2(a), O2(b), O(3P), I2, I(2P3/2), I(2P1/2), small-signal gain, and temperature. These measurements constrain the kinetics model of the system, and reveal the existence of new chemical loss mechanisms related to atomic oxygen. The results for O2(a) production at 1 kW have intriguing implications for the scaling of EOIL systems to high power.
This paper discusses methods, using non-intrusive diagnostic techniques, to characterize the detailed dynamics of I* gain and O2(a1Δ) yield on a laboratory microwave-discharge flow reactor, for conditions relevant to the electrically driven COIL concept. The key diagnostics include tunable diode laser absorption measurements of I* small-signal gain and temperature, high-precision absorption measurements of reactor I2 concentrations, absolute and relative spectral emission measurements of O2(a1Δ) and I* concentrations, and air-afterglgow determinations of O concentrations. We have characterized variations in O and O2(a) yields with discharge power and oxygen mole fraction. We observe O2(a) yields to increase dramatically with decreasing oxygen mole fraction. We have also demonstrated a spectral fitting analysis technique capable of quantifying the presence of vibrationally excited O2(a,v). This combined suite of diagnostics offers a comprehensive approach to performance characterization for electrically driven COIL concepts.
In this paper we discuss vibrational to electronic energy transfer as a potential method for producing a population inversion in atomic iodine. We discuss the background of this approach and a novel, high-flux F atom source integrated into a small scale supersonic reactor. We present data for energy transfer from HF(v) and H2(v) to the I atom manifold. Using a sensitive diode laser diagnostic we have probed the ground state manifold atomic iodine and observed that the absorption on the I atom line could be reduced to an immeasureably low value. We also describe a novel, diode laser based imaging diagnostic that will have important applications in future chemical or electrical laser development.
This paper presents results from investigations of mixing flowfields and optical gain profiles in HF chemical laser systems by infrared hyperspectral imaging. A chemiluminescent F + H2 reacting flowfield, produced in a high-fluence microwave-driven reactor, was imaged at a series of wavelengths, 2.6 to 2.9 μm, by a low-order, spectrally scanning Fabry-Perot interferometer mated to an infrared camera. The resulting hyperspectral data cubes define the spectral and spatial distributions of the emission. High-resolution images were processed to determine spatial distributions of the excited state concentrations of the product HF(v,J), as well as spatial distributions of small-signal gain on specific laser transitions. Additional high-resolution Fourier transform spectroscopy and spectral fitting analysis determined detailed excited state distributions in the reacting flowfield. The measurements confirm that our reactor generates inverted populations of HF(v,J).
We discuss a non-intrusive diagnostic for mixing, species concentration, and optical gain for HF chemical lasers. The instrument is based on hyperspectral imaging using a low order Fabry-Perot interferometer. The basic theory behind this technology is described and several applications to a chemically reacting flowfield are presented.
We present results from the early development of an F atom source appropriate for HF and AGIL chemical laser research. The system uses high power microwaves to produce a high enthalpy plasma that thermally dissociates molecular species such as SF6 and F2. Results of the characterization of the flow are presented.
We present a new ladar (laser radar) for the detection of objects off the line-of-sight. This is accomplished by a transceiver and a fiberoptic cable that relays an outgoing laser beam to, and a returning signal from a target. The transmission signal is a laser diode emitted beam at 1550 nm, ideal from the aspects of both eyesafety and minimum loss in a silica fiber. In our immediate application, the detection of an obstacle on the railroad track of a high-speed train, the laser pulses propagate through air and the fiberoptic cable, successively. Under a variety of simulated weather conditions and by traversing twice through a 2 km fiber, we measured a signal-to-noise of 300.
Although most optical materials are inert to the ambient low earth orbit environment, high velocity oxygen atoms will react with adsorbates to produce optical emissions from the ultraviolet into the infrared. The adsorbates arise from chemical releases or outgassing from the spacecraft itself. We have been investigating kinetic and spectral aspects of these phenomenon by direct observation of the 0.2 to 13 micrometers chemiluminescence from the interaction of a fast atomic oxygen beam with a continuously dosed surface. The dosing gases include fuels, combustion products and outgassed species such as unsymmetrical dimethylhydrazine (UDMH), NO, H2O and CO. The surface studied include gold and magnesium fluoride. In order to relate the results to actual spacecraft conditions these phenomena have been explored as a function of O atom velocity, dosant flux and substrate temperature. UDMH dosed surfaces exhibit spectra typical (wavelength and intensity) of carbonaceous surfaces. The primary emitters are CO, CO2, and OH. H2O dosed surfaces are dominated by OH and /or H2O emission while CO dosed surfaces are dominated by CO and CO2 emissions. The nitric oxide dosed surface produces a glow from 0.4 to 5.4 micrometers due to NO2* continuum emission. The emission was observed to increase by a factor of two upon cooling the surface from 20 degree(s)C to -35 degree(s)C.