Chemical Oxygen-iodine Laser Research Articles

Measurement of Small-Signal Gain on COIL With Chemically Generated Molecular Iodine

A chemical gas-phase reaction between <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Cl}_{2}$</tex></formula> and HI was used in the generation of molecular iodine for the chemical oxygen-iodine laser (COIL) operation. A yield of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm I}_{2}$</tex></formula> in the generation reaction up to 85% was achieved in a reasonable volume of the reactor. A small-signal gain up to 0.75%/cm at a temperature of 150 K in the center of supersonic cavity was measured. A comparison with the established evaporation way of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm I}_{2}$</tex></formula> delivery confirmed that the chemical method has little or no impact on the COIL pumping kinetics. This chemical method is easily scalable and can simplify the COIL operation by providing better control of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm I}_{2}$</tex></formula> flow rate.

Comparing modeling and measurements of the output power in chemical oxygen-iodine lasers: A stringent test of I2 dissociation mechanisms

A parametric study of the output power of supersonic chemical oxygen-iodine lasers (COILs) is carried out, applying a kinetic-fluid dynamics model calculations as well as an analytical model and comparing the results to experimental studies. The I(2) dissociation mechanism recently suggested by Azyazov et al. [J. Chem. Phys. 130, 104306 (2009)], which was previously used for comparison of model calculations to measurements of the small signal gain [K. Waichman et al., J. Appl. Phys. 106, 063108 (2009)], is applied here for a similar, but more sensitive, comparison of the laser output power. The dependence of the power on iodine flow rate and on mirror transmission is studied for low and high pressure COILs, respectively. Good agreement between the calculated and measured power is obtained for both low and high pressure COILs only when the processes suggested by Azyazov et al. are included in the calculations. This is different from the situation for the gain where for high pressure COILs, the calculated values were insensitive to the assumed dissociation mechanism, although for low pressure the measurements were reproduced only by applying the Azyazov et al. mechanism. We believe that the results of the present work strongly support the application of this mechanism for modeling the COIL operation.

Mixing in a supersonic COIL laser: influence of trip jets

We present an experimental study of a supersonic nozzle with supersonic iodine injection. This nozzle simulates Chemical Oxygen Iodine Laser (COIL) flow conditions with non-reacting, cold flows. During the experiments, we used a laser sheet near 565 nm to excite fluorescence in iodine, which we imaged with an intensified and gated CCD camera. We captured streamwise and semi-spanwise (oblique-view) images, with fluorescence revealing the material injected into the flow. We identified the flow structures in the images, and produced quantitative characterizations of the flow morphology and of the mixing between the primary and injected flow. We considered four injection scenarios. The first scenario includes a single injector positioned downstream of the nozzle throat. To enhance the mixing between the flows, trip jets are placed in the wake of the single jet. The sonic trip jets, significantly smaller than the primary supersonic iodine jet, are intended to destabilize the counter-rotating vortex pair (CRVP) of the primary jet. We compare three different trip jet configurations for their ability to enhance mixing between the oxygen and iodine flows.

Electrode system for electric-discharge generation of atomic iodine in a repetitively pulsed oxygen — iodine laser with a large active volume

Possibilities for increasing the active medium volume of a chemical oxygen — iodine laser (CCOIL) with a pulsed electric-discharge generation of atomic iodine are studied. The reasons are analysed of the low stability of the transverse self-sustained volume discharge in electrode systems with metal cathodes under the conditions of the electric energy input into gas-discharge plasma that are typical for CCOILs: low pressure of mixtures containing a strongly electronegative component, low voltage of discharge burning, low specific energy depositions, and long duration of the current pulse. An efficient electrode system is elaborated with the cathode based on an anisotropically-resistive material, which resulted in a stable discharge in the mixtures of iodide (CH3I, n-C3H7I, C2H5I) with oxygen and nitrogen at the specific energy depositions of ∼5 J L-1, pressures of 10 — 25 Torr, and mixture volume of 2.5 L.

Recent advances in the development of discharge‐pumped oxygen‐iodine lasers

AbstractChemical oxygen‐iodine lasers are unique in their ability to generate high‐power beams with near diffraction limited beam quality. The operating wavelength, 1.315 µm is readily transmitted by the atmosphere and compatible with fiber optics beam delivery systems. However, applications of the laser are severely limited by logistical problems associated with the complex chemistry used to power the device. Electrical or microwave discharge excitation of oxygen‐iodine lasers offers an attractive alternative that eliminates the chemical power generation problems and has the possibility of closed‐cycle operation. A discharge oxygen‐iodine laser was first demonstrated in 2005. Since that time the power of the device has been improved by a factor of 400 and much has been learned concerning the physics and chemistry of the discharge driven system. Although our current understanding of the chemical kinetics is incomplete, parametric studies of laser performance show considerable promise for further scaling. This article reviews the basic principles of the discharge oxygen iodine laser, summarizes the most recent advances, and outlines some of the unresolved questions regarding the production and removal of excited species in the gas flow.

Spray generator of singlet oxygen for a chemical oxygen-iodine laser

A spray type of singlet oxygen generator for driving the Chemical Oxygen-Iodine Laser was developed. Singlet oxygen, O2(1Δg), is generated by a fast reaction of chlorine with basic hydrogen peroxide solution in the form of a dense spray. A mathematical model of this reaction system showed that O2(1Δg) can be generated in this system with a high yield (0.70–0.80), high utilization of chlorine (0.75–0.95), and effective utilization of liquid (0.36–0.54) at very high generator pressures (35–75 kPa). Experimental studies of this reaction system without an efficient separation of liquid proved an efficient O2(1Δg) production characterized by a rather high product of chlorine utilization and O2(1Δg) yield (0.4–0.9) at very high generator pressures (30–80 kPa). This pressure is much higher than the operation pressure used in other generators, which should be beneficial for a pressure recovery system of the COIL. These results provided the basis for designing a centrifugal spray generator with an efficient separation of liquid from the gas flow, which is the subject of the following paper.

Centrifugal spray generator of singlet oxygen for a chemical oxygen-iodine laser

A centrifugal spray generator of singlet oxygen, O2(1Δg), for driving a chemical oxygen-iodine laser was developed and its operation was experimentally studied. Modeling of the liquid separation from the gas flow showed that the separator designed could remove droplets larger than 0.5 μm from gas, which is very important for the laser operation. This result was confirmed by experiments. Experimental studies proved that O2(1Δg) could be produced with a high efficiency (chlorine utilization 0.68–0.87 and O2(1Δg) yield 0.35–0.7) even at very high generator pressures (25–70 kPa), which cannot be attained by other O2(1Δg) generators.

Pressure recovery studies on a supersonic COIL with central ejector configuration

A chemical oxygen–iodine laser (COIL) is an electronic transition, low pressure, high throughput system. The field use of this laser demands the development of suitable pressure recovery systems. Ejector based pressure recovery systems form a potent alternative for open cycle COIL operation. The two possible configurations of motive gas injection in ejectors are peripheral and central. The present paper focuses on the investigation of a central injection low pressure ejector operated with a small scale supersonic COIL (SCOIL). The ejector handles a motive flow of nearly 120 g s −1 and an entrained laser flow of nearly 3 g s −1. The predicted geometry using integral methods has been validated numerically by employing Fluent 6.1 software in a 2-d axisymmetric viscous turbulent flow formulation. The numerical predictions have been experimentally validated, which indicate a pressure recovery of 63 Torr at design conditions. The results also show that the recovered pressure improves to 75 Torr for an off-design condition of higher motive flow rate.

On the origin of decomposition of triphenyl phosphite ozonide accelerated by ammonia or pyridine water solution

The decomposition of triphenyl phosphite ozonide (TPPO) has been well recognized as a potential source of singlet oxygen (O 2, 1Δ g) for the chemical oxygen–iodine laser. Experimental observations suggested that ammonia or pyridine water solution can accelerate the decomposition of TPPO, and hydroxyl ion is responsible for accelerating singlet oxygen liberation during this decomposition. In this paper, we studied the mechanism of OH −-accelerated reaction using density functional theory (DFT) at B3LYP/6-31+G* levels of theory. The calculations reveal a favorable free energy pathway for hydroxide-accelerated decomposition of TPPO, i.e. nucleophilic addition at phosphorus, followed by elimination of phenoxy group and subsequent liberation of singlet oxygen. The solvent effects were studied using a polarizable continuum model. The frontier molecular orbitals of the ozonides, atom–atom Wiberg bond index and corresponding atomic charges were also investigated to shed further light on the reaction pathway.

主流无载气N2-氧碘化学激光配气方式的数值优化

3-D Navier-Stocks equation with multi species and chemical reaction process was applied with CFD method on the chemical oxygen iodine laser(COIL) model using nitrogen as diluents gas to investigate the detailed flow field and the coupling between physical and chemical process, especially the appropriate mixing technique. It is found that mixing by jet in the subsonic section is inapplicable to the N2-COIL without primary buffer gas; jet in supersonic is necessary and with the appropriate flow rate ratio, the small signal gain could reach 1.5% cm-1 in the position of cavity; the efficient area of gain is widened since the thickness of boundary layer is reduced as the result of mixture weight increase.

Dynamical simulation of pulsed chemical oxygen-iodine laser

One-dimensional pre-mixed model for a pulsed chemical oxygen-iodine laser is presented according to the reaction mechanism in chemical oxygen-iodine laser. The dependence of species concentration and optical parameters on single pulse energy and pulse duration is studied. The dynamical process is analyzed while laser is running. Gain switching during lasing is discussed.These results can provide theoretical support for the optimization of pulsed chemical oxygen-iodine laser.

Development of a chemical oxygen — iodine laser with production of atomic iodine in a chemical reaction

The alternative method of atomic iodine generation for a chemical oxygen — iodine laser (COIL) in chemical reac-tions with gaseous reactants is investigated experimentally. The influence of the configuration of iodine atom injection into the laser cavity on the efficiency of the atomic iodine generation and small-signal gain is studied.

Research on chemical and discharge oxygen-iodine lasers

Novel methods and device configurations for singlet oxygen and atomic iodine generation were proposed and investigated for operation of the chemical or discharge oxygen-iodine lasers (COIL/DOIL). A chemical centrifugal spray generator of singlet oxygen was developed, based on the conventional chlorine-basic hydrogen peroxide chemistry. Results of theoretical and experimental investigation of the generator parameters are presented and compared with parameters of other generator types. A design of experimental device for singlet oxygen generation by means of the hybrid DC arc and RF plasma jet is presented. An alternative method of atomic iodine generation by a radiofrequency discharge decomposition of iodine compounds like CH3I or CF3I is described employing advanced experimental configuration. Some representative experimental results of this investigation are presented.

Pulse Operation of Chemical Oxygen-Iodine Laser by Pulsed Gas Discharge with the Assistance of Spark Pre-ionization

The continuous wavelength chemical oxygen-iodine laser can be turned into pulse operation mode in order to obtain high energy and high pulse power. We propose an approach to produce iodine atoms instantaneously by pulsed gas discharge with the assistance of spark pre-ionization to achieve the pulsed goal. The influence of spark pre-ionization on discharge homogeneity is discussed. Voltage-current characteristics are shown and discussed in existence of the pre-ionization capacitor and peaking capacitor. The spark pre-ionization and peaking capacitor are very helpful in obtaining a stable and homogeneous discharge. The lasing is achieved at the total pressure of 2.2–2.9kPa and single pulse energy is up to 180 mJ, the corresponding specific output energy is 1.0 J/L.

Kinetic-fluid dynamics modeling of I2 dissociation in supersonic chemical oxygen-iodine lasers

The mechanism of I2 dissociation in supersonic chemical oxygen-iodine lasers (COILs) is studied applying kinetic-fluid dynamics modeling, where pathways involving the excited species I2(X Σ1g+,10≤v&amp;lt;25), I2(X Σ1g+,25≤v≤47), I2(A′ Π32u), I2(A Π31u), O2(X Σ3g−,v), O2(a Δ1g,v), O2(b Σ1g+,v), and I(P21/2) as intermediate reactants are included. The gist of the model is adding the first reactant and reducing the contribution of the second as compared to previous models. These changes, recently suggested by Azyazov, et al. [J. Chem. Phys. 130, 104306 (2009)], significantly improve the agreement with the measurements of the gain in a low pressure supersonic COIL for all I2 flow rates that have been tested in the experiments. In particular, the lack of agreement for high I2 flow rates, which was encountered in previous models, has been eliminated in the present model. It is suggested that future modeling of the COIL operation should take into account the proposed contribution of the above mentioned reactants.

Crossed-beam intermodulated fluorescence spectroscopy as a spatially resolved temperature diagnostic for supersonic nozzles

A variant of laser saturation spectroscopy has been applied to the determination of spatially resolved temperature in low-pressure supersonic flows. By copropagating a pump and probe beam with a small crossing angle, the full Doppler profile is retained, but the signal is limited to the volume where both beams are overlapped. The technique was demonstrated on several rovibrational lines of the I2X1Sigma(0g+)-->B3Pi(0u+) transition in a Mach 2 Laval nozzle. A temperature of 146 K+/-1.5 K was extracted from measurements of the I2P(46) 17-1 spectral line with a spatial resolution of 2.4 mm3. Application of the technique to the turbulent gain medium of a chemical oxygen-iodine laser is discussed.

Analytic study of the chain dark decomposition reaction of iodides — atomic iodine donors — in the active medium of a pulsed chemical oxygen—iodine laser: 2. Limiting parameters of the branching chain dark decomposition reaction of iodides

The final stages in the development of a branching chain decomposition reaction of iodide in the active medium of a pulsed chemical oxygen—iodine laser (COIL) are analysed. Approximate expressions are derived to calculate the limiting parameters of the chain reaction: the final degree of iodide decomposition, the maximum concentration of excited iodine atoms, the time of its achievement, and concentrations of singlet oxygen and iodide at that moment. The limiting parameters, calculated by using these expressions for a typical composition of the active medium of a pulsed COIL, well coincide with the results of numerical calculations.

Supersonic diffuser for pressure recovery in SCOIL system

Classical supersonic chemical oxygen iodine laser (SCOIL) systems operate under a low total pressure of nearly 18 Torr (2400 Pa) with cavity pressure being in the range 3 Torr (400 Pa) and Mach number of 1.7. These systems handle high flow rates and hence an efficient supersonic diffuser (SD) is a critical first step towards an open-cycle operation, which may be followed by a multi-stage ejector system. The present study discusses the various aspects in the design of a supersonic diffuser for a twin 10 kW COIL module source which employs flow rates of 100 gs −1 in each module. The results of computational studies based on 3-D, viscos compressible flow, k– ε turbulence formulation for the supersonic diffuser geometry have also been discussed. The experimental results from a single-module test of the supersonic diffuser show that a total recovered pressure of nearly 7 Torr is achieved at the diffuser exit.

Novel concept of electric discharge oxygen-iodine laser

A novel concept of discharge oxygen-iodine laser (DOIL) is presented. The supersonic DOIL includes a discharge singlet oxygen generator (DSOG) and discharge atomic iodine generator (DAIG). The operation of DSOG is based on a fast mixing of hybrid argon plasma jet of DC electric arc and RF discharge with a neutral molecular oxygen stream. The goal of our effort is achievement of DOIL oscillations by this new discharge technique, which should provide the singlet oxygen yields exceeding 30% at the total pressures higher than 10 torr. The DAIG operation is based on a cw/pulse RF discharge dissociation of iodine donors directly inside a laser iodine injector. This method substitutes the classic dissociation of molecular iodine by energy of singlet oxygen, which saves its energy for laser generation and so can increase the laser efficiency. The laser power could be thus enhanced by up to 25% if this method is employed in a chemical oxygen-iodine laser (COIL) operation, and even 3 times in DOIL without increase in the iodine laser pumping by singlet oxygen.

Analysis of lasing in chemical oxygen-iodine lasers with unstable resonators using a geometric-optics model

A simple geometric-optics model is developed that describes the power extraction in chemical oxygen-iodine lasers (COILs) with unstable resonators. The positive and negative branch unstable resonators with cylindrical mirrors that were recently used in COILs are studied theoretically. The optical extraction efficiency, spatial distributions of the intracavity radiation intensity in the flow direction, and the intensity in the far field are calculated for both kinds of resonator as a function of both the resonator and the COIL parameters. The optimal resonator magnifications that correspond to the maximum intensity in the far field are found.