This paper presents the development and initial experimental testing of a new compact, high-performance singlet oxygen generator (SOG). The generator uses a centrifugal design to assist in two-phase separation, a porous plate injection technique to create a froth and maximize chlorine utilization, and a closely coupled minimum length nozzle (MLN) to minimize transport losses. A high froth speed in the curved wall region is essential in order to attain a significant centrifugal force that pins the liquid component to the curved wall, which consequently results in a rapid and efficient separation of the vapor containing the excited oxygen that then flows into the nozzle. This generator operates without diluent and was demonstrated to perform at pressures greater than 350 Torr, which enables the technology to operate without the need for a pressure recovery system in an airborne chemical oxygen-iodine laser (COIL). The implementation of this froth SOG (FSOG) in combination with the use of a MLN allows the generation of large number densities of excited oxygen at a very high plenum pressure without the use of any diluent. Experimental results for this novel FSOG, along with the engineering logic behind it, are presented. Number densities greater than 5.3×1017 cm–3 were measured via calibrated spectroscopic analysis of the O2(1 Δ) emission about 1268 nm at the exit of a supersonic nozzle. To the authors’ knowledge, the FSOG produced a higher pressure and larger excited oxygen number density than any other SOG system reported.
Experiments operating a Cs D2 line (852.1 nm: 62P3/2→62S1/2) laser, pumped by blue wing absorption of different thermal Cs-rare gas ground state pairs, were analyzed. Using a 10 cm sealed gas cell, the D2 line laser performance is highest for Cs-Ar at 513K, and for Cs-Kr and Cs-Xe at 473 K. Overall, the highest optical-to-optical efficiency measured was 1.1% with a linear slope efficiency of 1.5% for the Cs-Ar collision pair at 513 K. All three Cs-rare gas mixtures show a D2 line laser performance increase with temperature towards a peak efficiency, followed by a decrease as temperature is increased beyond the peak performance point. At lower temperatures ≤453 K the efficiency was highest with Cs-Xe, at 473 K highest with Cs-Kr, whereas at higher temperatures ≥ 493 K the efficiency was highest with Cs-Ar. Measurement of the reduced absorption coefficient for the peak of the blue satellite of the different collision pairs resulted in values of 1.2∙10-36 cm5 for Cs-Ar at 836.7 nm, 2.0∙10-36 cm5 for Cs-Kr at 841.1 nm, and 3.0∙10-36 cm5 for Cs-Xe at 842.7 nm. Simulations of the data using the detailed BLAZE Multiphysics software suite were also performed, which aid in the understanding of the basic physics behind the XPAL system. The simulations indicate that energy pooling significantly inhibits laser performance at higher temperatures above 500 K.
Experiments[1] with Electric Oxygen-Iodine Laser (ElectricOIL) heat exchanger technology have demonstrated improved control of oxygen atom density and thermal energy, with minimal quenching of O2(a1Δ), and increasing small signal gain from 0.26% cm-1 to 0.30% cm-1. Heat exchanger technological improvements were achieved through both experimental and modeling studies, including estimation of O2(a1Δ) surface quenching coefficients for select ElectricOIL materials downstream of a radio-frequency discharge-driven singlet oxygen generator. Estimation of O2(a1Δ) quenching coefficients is differentiated from previous studies by inclusion of oxygen atoms, historically scrubbed using HgO[2-4] or AgO[5]. High-fidelity, time-dependent and steady-state simulations are presented using the new BLAZE-VI multi-physics simulation suite[6] and compared to data.
Continuing experiments with Electric Oxygen-Iodine Laser (EOIL) technology have significantly increased laser power
output by increasing the product of gain and gain-length, g0L. Increasing the system size by a factor of 3 resulted in a 5-fold increase in laser output on the 1315-nm transition of atomic iodine. The peak output power observed was 538 W.
Continuing experiments with Electric Oxygen-Iodine Laser (ElectricOIL) technology have significantly increased laser
power output by increasing the product of gain and gain-length, g0L. The authors report on progress with recent
ElectricOIL devices utilizing a new concentric discharge geometry with improved O2(a1▵) production at higher
discharge operating pressure at higher system flow rates. O2(a1▵) produced in flowing radio-frequency discharge in O2-
He-NO gas mixture is used to pump I(2P1/2) by near-resonant energy transfer, and laser power is extracted on the I(2P1/2)
→ I(2P3/2) transition at 1315 nm. Modeling of recent data is presented. By increasing the gain length (system size) by a
factor of 3, a 5-fold increase in laser output on the 1315-nm transition of atomic iodine was achieved. Flow conditions
with g0L = 0.042 were used to extract a continuous wave (CW) average total laser power of 481 W. A low frequency
±11.9% oscillation in the total power was observed giving a peak outcoupled power of 538 W.
KEYWORDS: Laser resonators, Iodine, Data modeling, Electrodes, Laser systems engineering, Performance modeling, Oxygen, Quartz, Light emitting diodes, Chemical species
Experiments and modeling have led to a continuing evolution of the Electric Oxygen-Iodine Laser (ElectricOIL) system.
A new concentric discharge geometry has led to improvements in O2(a) production and efficiency and permits higher
pressure operation of the discharge at high flow rate. A new heat exchanger design reduces the O2(a) loss and thereby
increases the O2(a) delivered into the gain region for a negligible change in flow temperature. These changes have led to
an increase in laser cavity gain from 0.26% cm-1 to 0.30% cm-1. New modeling with BLAZE-V shows that an iodine
pre-dissociator can have a dramatic impact upon gain and laser performance. As understanding of the ElectricOIL
system continues to improve, the design of the laser systematically evolves.
Experiments and modeling have led to a continuing evolution of the Electric Oxygen-Iodine Laser (ElectricOIL) system.
This continuous wave (cw) laser operating on the 1315 nm transition of atomic iodine is pumped by the production of
O2(a) in a radio-frequency (RF) discharge in an O2/He/NO gas mixture. New discharge geometries have led to
improvements in O2(a) production and efficiency. Further, size scaling is presently showing a super-linear growth in
performance; a 95% enhancement in cw laser power was achieved via a 50% increase in gain length, flow rates, and
discharge power. New gain recovery measurements and modeling downstream of an operating laser cavity are presented
in this work for a wider range of flow conditions to help identify previously unidentified kinetic processes. Larger
volume resonators that extend further downstream in the flow direction were able to extract more of the excess energy
being carried by the O2(a) from the ElectricOIL gain medium; a further 87% increase in extracted laser power was
obtained. As understanding of the ElectricOIL system continues to improve, the design of the laser systematically
evolves. The gain has improved by more than 100-fold from the initial demonstration of 0.002% cm-1 to 0.26% cm-1,
and similarly the outcoupled laser power has increased more than 600-fold from 0.16 W to 109 W.
Experiments and modeling have led to continued enhancements in the Electric Oxygen-Iodine Laser (ElectricOIL)
system. This continuous wave (cw) laser operating on the 1315 nm transition of atomic iodine is pumped by the
production of O2(a) in a radio-frequency (RF) discharge in an O2/He/NO gas mixture. New discharge geometries
have led to improvements in O2(a) production and efficiency. A 95% enhancement in cw laser power was achieved
via a 50% increase in gain length, flow rates, and discharge power. A further 87% increase in extracted laser power
was obtained using a larger mode volume resonator. The gain has improved by more than 100-fold from the initial
demonstration of 0.002% cm-1 to 0.26% cm-1, and similarly the outcoupled laser power has improved more than
500-fold from 0.16 W to 102 W.
Systematic experiments have led to continued improvements in the hybrid Electric Oxygen-Iodine Laser (ElectricOIL)
system that significantly increased the discharge performance, supersonic cavity gain, and laser power output.
Experimental investigations of radio-frequency (rf) and pulser-sustainer (ps) discharges in O2/He/NO mixtures in the
pressure range of 10-50 Torr and power range of 0.1-2.0 kW have shown that O2(a1Δ) production is a strong function of
geometry, pressure and diluent ratio. In our investigations, transverse rf discharges always resulted in higher
performance (by all metrics) than did the ps discharges tested. Results with both molecular iodine injection and partially
pre-dissociated iodine are presented. A gain of 0.17% cm-1 was measured with a corresponding outcoupled power of
12.3 W (with a 5 cm cavity). Modeling with the BLAZE-V model is in good agreement with discharge and gain data,
but significantly overpredicts laser power. This modeling result has led to an interesting investigation of power
extraction questions for the ElectricOIL system; these studies include measurements of gain recovery downstream from
the laser cavity and estimates of the role that diffractive losses play in our small cavity with high mirror reflectivities.
Recent investigations of an Electric Oxygen-Iodine Laser system have shown that computational modeling over-predicts
the laser power output measured in experiments for similar gain conditions. To help resolve this
discrepancy, detailed 2-axis mapping of gain and gain recovery measurements downstream of an operating laser
cavity were performed. Modeling and analyses of the gain recovery experiments indicate that when the pumping rate
of I(2P1/2) by O2(a1Δ) is reduced by an effective factor of approximately 4 as a result of an unknown competing
reaction, the calculations are well matched to the experimental gain recovery measurements. The agreement
between the measured and modeled laser power extraction also significantly improves when the reduced effective
pumping rate is used. The results suggest that there may be a competing reaction that effectively reduces the
forward pumping rate as compared to the classical chemical oxygen-iodine laser kinetics rates. Understanding of
this kinetic process should enable us to accommodate or eliminate its impact on ElectricOIL performance.
Herein the authors report on the demonstration of gain and a continuous-wave laser on the 1315 nm transition of atomic
iodine using the energy transferred to I(2P1/2) from O2(a1Δ) produced by both radio-frequency and microwave electric
discharges sustained in a dry air-He-NO gas mixture. Active oxygen and nitrogen species were observed downstream of
the discharge region. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower
the temperature of the continuous gas flow. Gain of 0.0062 %/cm was obtained and the laser output power was 32 mW
in a supersonic flow cavity.
Experimental investigations of radio-frequency discharges in O2/He/NO mixtures in the pressure range of 1-100
Torr and power range of 0.1-2.5 kW have indicated that O2(a1Δ) production is a strong function of geometry,
pressure and diluent ratio. The goal of these investigations was maximization of both the yield and flow rate (power
flux) of O2(a1Δ) in order to produce favorable conditions for application to an electric oxygen-iodine laser (EOIL).
As pressure is increased, yield performance is dominated by the influence of geometry and diluent ratio. Numerous
measurements of O2(a1Δ), oxygen atoms, and discharge excited states are made in order to describe the discharge
performance dependence on various parameters.
Experimental investigations of radio-frequency discharges in O2/He/NO mixtures in the pressure range of 1-100
Torr and power range of 0.1-1.2 kW have indicated that O2(a1Δ) production is a strong function of geometry,
excitation frequency, pressure and diluent ratio. The goal of these investigations was maximization of both the yield
and flow rate (power flux) of O2(a1Δ) in order to produce favorable conditions for application to an electric oxygen-iodine
laser (EOIL). At lower pressures, improvements in yield are observed when excitation frequency is increased
from 13.56 MHz. As pressure is increased, increasing excitation frequency in the baseline configuration becomes
detrimental, and yield performance is improved by reducing the discharge gap and increasing the diluent ratio.
Numerous measurements of O2(a1Δ), oxygen atoms, and discharge excited states are made in order to describe the
discharge performance dependent on various parameters.
In the hybrid electric discharge Oxygen-Iodine laser (ElectricOIL), the desired O2(a1&Dgr;) is produced using a low-to-medium pressure electric discharge. The discharge production of atomic oxygen, ozone, and other excited species adds higher levels of complexity to the post-discharge kinetics which are not encountered in a classic purely chemical O2(a1&Dgr;) generation system. Experimental studies over the past six years using electric discharges have demonstrated O2(a) yields greater than 20%, gain, and cw laser power. Several modeling studies have also been performed for ElectricOIL and similar systems. As the development of this type of iodine laser continues, the roles of oxygen atoms and NO/NO2 are found to be very significant in both the discharge region and downstream of the discharge region. A series of O2(1&Dgr;) emission, I* emission, O-atom titrations, gain, and O2(1&Dgr;) yield, NO2* emission, and laser power measurements have been taken to explore the complex phenomena that are being observed. As the overall system is better understood improvements are being made in laser power and efficiency.
Laser oscillation at 1315 nm on the I(2P1/2) → I(2P3/2) transition of atomic iodine has been obtained by a near
resonant energy transfer from O2(a1&Dgr;) produced using a low-pressure oxygen/helium/nitric-oxide discharge. In the
electric discharge oxygen-iodine laser (ElectricOIL) the discharge production of atomic oxygen, ozone, and other
excited species adds levels of complexity to the singlet oxygen generator (SOG) kinetics which are not encountered
in a classic purely chemical O2(a1&Dgr;) generation system. The advanced model BLAZE-IV has been introduced in
order to study the energy-transfer laser system dynamics and kinetics. Levels of singlet oxygen, oxygen atoms and
ozone are measured experimentally and compared with calculations. The new BLAZE-IV model is in reasonable
agreement with O3, O2(b1&Sgr;), and O atom, and gas temperature measurements, but is under-predicting the increase in
O2(a1&Dgr;) concentration resulting from the presence of NO in the discharge. A key conclusion is that the removal of
oxygen atoms by NOX species leads to a significant increase in O2(a1&Dgr;) concentrations downstream of the discharge
in part via a recycling process, however there are still some important processes related to the NOX discharge
kinetics that are missing from the present modeling. Further, the removal of oxygen atoms dramatically inhibits the
production of ozone in the downstream kinetics.
Laser action at 1315 nm on the I(2P1/2) → I(2P3/2) transition of atomic iodine has been obtained by a near resonant energy
transfer from O2(a1Δ) produced using a low-pressure electric discharge. In the electric discharge oxygen-iodine laser
(ElectricOIL) the discharge production of atomic oxygen, ozone, and other excited species adds significantly higher
levels of complexity to the post-discharge kinetics which are not encountered in a classic purely chemical O2 (a1Δ)
generation system. In this paper, the discharge species output for laser operating conditions are discussed. Spatial
measurements of O2(a1Δ) and O2 (b1Σ) are reported, and various methods for the determination of atomic oxygen levels
are discussed and compared. The injection of NOX into the system to benefit O2(a1Δ) production is investigated.
In this paper we report on studies of a continuous wave laser at 1315 nm on the I(2P1/2) → I(2P3/2) transition of atomic iodine where the O2(a1▵) used to pump the iodine was produced by a radio frequency excited electric discharge. The electric discharge was sustained in He/02 gas mixtures upstream of a supersonic cavity which is employed to lower the temperature of the continuous gas flow and shift the equilibrium of atomic iodine in favor of the I(2P1/2) state. The results of experimental studies for several different flow conditions and mirror sets are presented. The highest laser output power obtained in these experiments was 510 mW in a stable cavity composed of two 99.993% reflective mirrors. Blaze II laser model was used to model typical ElectricOIL conditions in the post-discharge region through the laser cavity. Overall the Blaze II simulation model appears to be predicting many of the observed qualitative trends that have been measured and the quantitative comparisons to data are reasonable.
As the development of the electric discharge iodine laser continues, the role of oxygen atoms downstream of the discharge region was found to be very significant. One of the largest uncertainties is the rate of the quenching of I* by O atoms. We have taken a series of measurements of O2(1Δ) emission, I* emission, O-atom titrations, gain/absorption, and O2(1Δ) yield to explore the significant positive and negative roles that O atoms play in the kinetics of the system that influence the gain. An estimate of the reaction rate for I* + O is provided. This investigation of the effects of atomic oxygen led to the measurement of positive gain on the 1315 nm transition of atomic iodine where the O2(a1Δ) was produced in a flowing electric discharge. Excess atomic oxygen was scavenged by NO2 to minimize the deleterious effects. The discharge production of O2(a1Δ) was enhanced by the addition of a small proportion of NO to lower the ionization threshold of the gas mixture. The electric discharge was followed by a continuously flowing supersonic cavity, which was employed to lower the flow temperature.
Theoretical studies have indicated that sufficient fractions of O2 (1Δ) may be produced in an electrical discharge that will permit lasing of an electric discharge oxygen-iodine laser (ElectriCOIL) system in conjunction with injection of pre-dissociated iodine. Results of those studies along with more recent experimental results show that electric excitation is a very complicated process that must be investigated with advanced diagnostics along with modeling to better understand this highly complex system. In this paper, recent work in the development of the ElectriCOIL system is discussed. A kinetic package appropriate for the ElectriCOIL system is presented and implemented in the detailed electrodynamic GlobalKin model and the Blaze II laser modeling code. A parametric study with the Blaze II model establishes that it should be possible to attain positive gain in the ElectriCOIL system, even with subsonic flow. The Blaze II model is in reasonable agreement with early gain data. Temperature is a critical flow variable, especially in the subsonic cases. Simulations of a supersonic ElectriCOIL system indicate that significant performance levels can be attained, even at low yield levels of 20% or less. In addition, pre-dissociation of the iodine is also shown to be very important for the supersonic flow situation. Given the critical nature of the temperature issue, it appears that supersonic flow will be required for the ElectriCOIL system to achieve significant performance levels, but these simulations also indicate that it should be possible to demonstrate a subsonic system.
Modeling studies have shown that fractions of O2(1Δ) may be produced in an electrical discharge that will enable oscillation of a chemical oxygen-iodine laser system in conjunction with injection of pre-dissociated iodine. Results of those studies along with recent experimental results indicate that generation of O2(1Δ) can be optimized by the addition of flow diluents and select choice of process parameters. The model predicts the experimentally observed spatial decay of O2(1Σ) and shows reasonable agreement with experimentally observed temperatures.
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