The demonstration and characterization of a multiwatt All Gas-phase Iodine Laser (AGIL) are described. A 20-cm subsonic reactor was used to produce NCl(a1Δ) for a series parametric studies of the I*(2P1/2) - I(2P3/2) small signal gain and extracted power dependence on reactant flow rates and reaction time. A reduction in the flow channel height led to improved performance. The highest measured gain was 4.2 x 10-4 cm-1 and the highest power observed was 31 W.
The reactions of NCl3 have been studied with the aim of assessing the potential for an NCl3 fueled NCl(a) - I transfer chemical laser. In this set of experiments we are looking at the chlorine atom initiated decomposition of NCl3 and it's subsequent reaction with hydrogen.
In this paper we present results from a spectroscopic and kinetic study of the reaction sequence of NCl3 + H that produces NCl(a1Δ). Using sensitive optical emission diagnostics, we have observed both NCl(a) and (b) produced by this reaction. Upon addition of HI to the flow, the reaction of H + HI produced iodine atoms that were pumped to the excited I(2P1/2) state, and we observed strong emission from the I atom 2P1/2 → 2P3/2 transition at 1.315 μm. We also used a sensitive diode laser spectrometer to probe the I atom transition and observed transfer of population from ground state (2P3/2) to the excited state (2P1/2) with a concomitant reduction in the measured absorption. We interpret this observation as an approach to optical transparency.
Measurements of NCl(a) kinetics are being carried out in support of the effort to develop an NCl(a) driven iodine laser. Photolysis of ClN3 has been used as a radical source in several previous kinetic studies, as this produces high yields of NCl(a). It had been assumed that NCl(a) was a primary photoproduct. Measurements made under collision-free conditions now indicate that NCl(a) is a minor product, and that Cl and N3 are produced with a branching fraction of 0.95. In the present study we show that NCl(a) is efficiently produced by secondary photochemical reactions when ClN3 is photolyzed at moderate pressures. The implications of this finding for kinetic studies that rely on photolytic NCl(a) generation are considered.
The effect of temperature on NCl(a) quenching rate constants is being investigated because the NCl(a)/I laser operates at elevated temperatures (>400 K). Quenching by H2, HCl, Cl2, and O2 in the temperature range from 295-460 K has been examined in the present study.
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.
Theoretical models for the chemical lasers depend on a variety of assumptions and empirical data to provide closure and simplify solution of the governing equations. Among the various assumptions and empirical data built into models for chemical lasers are assumptions regarding steadiness in the time domain and geometric similarity of the computational domain. The work discussed here is directed toward elucidating and increasing the understanding of the assumptions underlying chemical laser models and the implications for the modeled physical processes underlying the chemical laser, driven by current directions in the development of this technology. This is directly linked to efforts to achieve improved chemical laser efficiencies and performance, as excursions outside the assumed to be ‘well understood’ traditional operational parameter space are increasingly necessary.
Dissociation of I2 by O2(b) is a process that is potentially important in iodine laser systems that are driven by discharge and chemical singlet oxygen generators. Recent work on the quenching of singlet oxygen by I2 suggests that the accepted upper bound of <0.2 for the branching fraction for O2(b) + I2 → O2(X) + 2I may be too low. New measurements of the branching fraction have been carried out using transient diode laser absorption technique to monitor I atom formation. The results indicate that the branching fraction may be as high as 0.6.
A cross flow jet SOG has been developed in Miki Pulley Co. Ltd. to supply O2(1D) for different types of COILs. Performance testing of the SOG has been conducted through a wide range of gas pressures (5~40 Torr), specific surface areas (4~7 cm-1), gas velocities (5~30 m/s), and gas temperatures to characterize and optimize the device. The inflow and out flow of the reactants and products, including O2(1D), Cl2, H2O were measured using optical and conventional techniques. The gas temperatures in the measurement duct were estimated from stagnation pressures, mass flow rates, and critical cross section at the gas chocking point in order to determine the partial pressures of the gas products at the measurement point. Calibration method of the O2(1D) measurement suggested by Zagidullin is basically employed with a slight correction of upper limit definition of O2(1D) yield associated with the pooling loss, which remains even at the minimum P t condition of our device. Assuming that the gas temperature after passing through the jets is equilibrium with that of the BHP jets (-18 degree Celsius) in our calibration condition, the upper limit yield can be derived from the increase in the gas temperature. The estimated value of the yield limit was 94 %. A wide range of output values (40-95 % of Cl2 utilization, 50-90 % of O2(1D) yield) was obtained and analyzed to characterize the device. As a result of optimization, a 27 % of chemical efficiency was obtained when Cl2 utilization was 95 %, O2(1D) was 90 %, O2 partial pressure was 6.7 Torr, and N2 dilution ratio was 2. Discussion on the validity of the gas temperature estimation method is provided by comparing the results to the heat release based on the pooling model.
Collision-induced absorption spectra have been measured in a wide temperature (80 - 300 K) and pressure (10 - 150 atm) range for the a ← X and b ← X absorption bands of oxygen. The peak and integrated absorption coefficients and monomolecular and multimolecular collision-induced cross-sections are measured for an oxygen density range of 4x1020 cm-3 to liquid. No temperature dependence was found in the absorption of the high density oxygen.
Preliminary measurements of the yield of O2(1Δ) as a function of power absorbed in an RF discharge are presented. The yield is deduced from measurements of gain/absorption using the PSI Iodine Scan diagnostic coupled with a data reduction technique originally developed by PSI. A more formal presentation of the method of deducing the yield is provided. Atomic oxygen titration experiments are presented along with gain as a function of power input to the system.
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.
A kinetics model to describe the behavior of singlet delta O2 in optically pumped liquid oxygen has been developed and tested against experimental data. The model was developed to study alternative methods of O2(a1Δg) production for the Chemical Oxygen Iodine Laser (COIL), and has been used in conjunction with experimental data to determine a value for the pooling rate constant in liquid oxygen of 1± 0.5 x 10-17 cm3molecule-1s-1.
Electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures at gas pressures up to 100 Torr was experimentally studied in large excitation volume (~18 liter). The discharge in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amount of carbon monoxide or hydrogen, the electric stability of the discharge increases, specific input energy per molecular component being higher more than order of magnitude and coming up to 6.5 kJ/(l atm). Theoretical calculations demonstrated that for the experimental conditions the singlet delta oxygen yield may reach ~20% exceeding its threshold value needed for oxygen-iodine laser operation at room temperature. The results of experiments on spectroscopy of the singlet delta and singlet sigma oxygen states in the EBSD are presented.
Overtone small signal gain data measured while operating a small-scale HF laser saturated on the fundamental transitions are compared with fundamental lasing output spectra and spontaneous overtone emission spectra measured orthogonal to the lasing axis. In all cases, the data are consistent with an equilibrium rotational distribution. These results are discussed in terms of their applicability to the question of rotational nonequilibrium in cw HF lasers.
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).
The small signal gain of a small-scale HF overtone laser was measured using a sub-Doppler tunable diode laser system. Measurements of reactant concentration, flow velocity and gain length were also made. The spatially resolved, two-dimensional small signal gain and temperature maps that were generated show a highly inhomogeneous gain medium indicating the dominant role played by mixing of the H2 and F streams in HF laser performance. The measured gain and temperature data were analyzed with the aid of a two-dimensional computational fluid dynamics model. The results show that reactant mixing mechanisms have a large effect on the gain averaged over a vertical profile while kinetic rate mechanisms, including reaction rate constants and reactant concentration, have a greater effect on the maximum system gain.
DPAL, a new class of diode pumped alkali vapor lasers, offers the prospect for high efficiency cw laser radiation at near-infrared wavelengths: cesium 895 nm, rubidium 795 nm, and potassium 770 nm. The physics of DPAL lasers are outlined, and the results of laboratory demonstrations using a titanium sapphire surrogate pump are summarized, along with benchmarked device models. DPAL electrical efficiencies of 25-30% are projected and near-diffraction-limited DPAL device power scaling into the multi-kilowatt regime from a single aperture is also projected.
Results of experimental investigation of the chemical generation of atomic iodine for a Chemical Oxygen-Iodine Laser (COIL) are presented. The work was focused on the reaction system with atomic fluorine as an intermediate species produced by the chemical way from gaseous reactants. At the first step, atomic fluorine is produced in reaction of molecular fluorine with nitrogen oxide. Then F atoms react with gaseous hydrogen iodide producing atomic iodine. The efficiency of this two-step process was studied thoroughly in dependence on mixing conditions, flow rate of reacting gases and pressure in the reactor. The results obtained on the small-scale device under experimental conditions simulating pressure and flow conditions in a COIL show that atomic iodine is generated by this alternative, advantageous method with rather high concentrations sufficient for operation of the supersonic COIL.
The production of high power, high efficiency, high specific energy and high optical beam quality can be obtained in the experimental systems of a quasi-cw electroionization CO laser with cooling a CO mixture by its expansion in the nozzles. The way of transfer to industrial high-power CO lasers is proposed through the continuous formation of a CO laser mixture during laser operation. CO laser mixture is formed by using air as a buffer gas (about 90%). CO molecules are generated in oxidation reaction of oxygen-containing molecules with carbon. The carbon arises from a decomposition of hydrocarbon fuel on the catalyst surface. CO mixture is excited by radio-frequency (RF) electric discharge in supersonic gas flow without an electron gun. The given conception was used on a small-scale model system to demonstrate that the laser radiation was possible in a CO mixture with combustion products and air, which are excited by RF discharge in a supersonic flow. The industrial CO-laser with power 20÷40kW is designed with open working cycle without ejecting toxing CO into the atmosphere by converting CO molecules to CO2 ones.
Analysis of heat release into operative gas of Chemical Oxygen Iodine Laser (COIL) is discussed. Pooling reaction of oxygen molecules in the excited state, the iodine dissociation process and the interaction of them with water vapor release energy of in the excited state oxygen molecules as heat energy. As results of heat release in the plenum, a rise of the total pressure as a rise of the total temperature is observed, and in the supersonic region a rise of static pressure and a decrease of total pressure as a rise of total temperature are observed. By following our analysis technique regarding pressure data of three different nozzles, the evaluations such as energy loss in a duct from a Singlet delta Oxygen
Generator (SOG) and the number of dissipated oxygen molecules for the iodine dissociation can be estimated.
The high power excimer laser was developed. We have supplied the 240 watts (800 mJ, 300 Hz) average power excimer laser for industrial use, mainly for TFT LCD annealing. We are going to add the 300 watts (1 J, 300 Hz) average power laser for our line-up. This 300 watts new laser is based on the 240 watts laser, but improved some points. The electrodes size is longer and the electrical power circuit is reinforcement. Laser gas recipe is changed to be good for new system. In our test, we could oscillate over 300 watts average power operation. 310 watts servo operation is able to oscillate over 40 million pulses with less than 1.0 per cent for σ output stability. 330 watts servo operation is able to oscillate over 30 million pulses with almost less than 1.0 per cent for σ output stability. Experimental and theoretical studies of various parameters influencing the laser performance will be continued with
further investigations and future improvements. We have confidence that it will be possible for this laser to produce higher power with long gas life.