Chemical Laser System Research Articles

Highly sensitive gas refractive index sensor based on hollow-core photonic bandgap fiber.

A highly sensitive gas refractive index (RI) sensor based on hollow-core photonic bandgap fiber (HC-PBF) and Fourier transform white-light interferometry was experimentally demonstrated. HC-PBFs with lower loss than hollow silica tubes render a longer air cavity for the Fabry-Perot interferometers (FPIs) without a great deal of compromise to the fringe visibility of interference. Fourier transform phase demodulation method was employed in the experiment and a directly proportional relationship between the phase sensitivity and cavity length was demonstrated. For a cavity length of ∼24.9 mm, the sensor's gas RI sensitivity reaches up to 50775.54 µm/RIU in an air RI range from 1.000 to 1.030. Considering the cavity length demodulation resolution of 0.06 µm achieved by this method, the sensor can detect gas RI change with a resolution of 10-6 RIU, which can meet the sensing demand for almost all the gases. Moreover, the gas RI sensitivity and measurement range can be improved further by lengthening the HC-PBF. The high sensitivity, large dynamic range and good linearity of the proposed sensor make it a good candidate for biosensing, monitoring of modern chemical industry or gas laser systems.

Optimal design for the support structure of a cavity mirror in a chemical oxygen iodine laser resonator.

The dynamic characteristics of the cavity mirror support structure strongly influence the quality of the output beam. However, the contradiction between excellent dynamic performance and light weight make the design process challenging. To cope with the problems encountered in the original design of a chemical oxygen iodine laser system, this paper presents a two-dimensional adjustable support structure based on spherical constraints with large specific stiffness in the initial design phase. Subsequently, a two-level optimization strategy containing a macro design and a detailed design is adopted to optimize the initial structure. At the macro design stage, a two-step topology optimization procedure is introduced, in which the scale of the optimization model is dramatically reduced using the independent continuous mapping algorithm to improve the calculation speed in the first step, and the gray elements are eliminated using the bi-directional evolutionary structural optimization method to clearly obtain the optimal topology in the second step. This method is verified to overcome the defect of low efficiency, while still eliminating gray elements. At the detailed design stage, an adaptive surrogate model and the multi-objective design optimization method are employed to seek the best compromise between the lower weight and higher dynamic performance. The results from the application to the example of the cavity mirror support structure show that the mass is reduced by 41.8%, and the dynamic performance requirement is fulfilled.

A Chemosorption Vacuum Pump for a Chemical Oxygen Iodine Laser with CO2 Buffer Gases

We present the design and investigation of a novel chemosorption vacuum pump (CSVP) for discharging the exhaust gases of a chemical oxygen-iodine laser system diluted with carbon dioxide (CO2-COIL). The CSVP comprises two fixed-bed reactors separately filled with CO2/H2O and O2/I2/Cl2 adsorbents, which can efficiently chemically absorb the CO2-COIL exhaust gases at room or higher temperature. We consider the effects of the adsorbents in different specifications and fixed beds of various constructions on the adsorption performance of the CSVP. We develop and study the sealed CO2-COIL system with the CSVP. We achieve a stable operation with a cumulative duration time of 40 s for four runs and an average output power up to 2.0 kW at a Cl2 flow rate of ∼158 mmol/s and a CO2 flow rate of 132 mmol/s. The experimental results indicate that the COIL system with the CSVP performs similarly to a conventional COIL with a vacuum tank. Taking into account that the CSVP is free of vibration and noise, avoids air pollution, is easily operated, and has a short preparation time, we believe that the chemosorption vacuum pump is an excellent alternative pump system for a transportable COIL system.

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.

Variation of population inversion and gain characteristics with D2 injection angle in DF chemical laser cavity

Nowadays, a chemical laser has been developed not only for a strategic military purpose, but also as a manufacturing tool in industrial usage due to its high power lasing characteristics. In order to increase the laser beam power in the chemical laser systems, the mixing efficiency of fuel and oxidant should be improved, since more excited molecules are followed by high mixing efficiency. Basically, the production of a lot of excited molecules in the laser cavity results from the high mass flow rates of fuel and oxidant based on efficient mixing and chemical reaction. Therefore, in order to supply higher mass flow to the chemical laser cavity, a radial-expansion nozzle array was used and examined here, not a planar nozzle array which has been widely employed until now. The laser beam generation in this system is achieved by mixing F atoms from supersonic nozzle with D 2 molecules ejecting from holes of round-bended supply lines which are distributed in zigzag configuration, which would extend the reaction zone. Consequently, more excited molecules are expected to be produced, so the intensity of population inversion will be higher. Since the two-stream injection angle was considered to influence the performance of supersonic combustor, the effects of D 2 injection angles against the main F flow on mixing enhancement, population inversion and gain characteristics were numerically investigated in this study. The results were discussed by comparison with three cases of D 2 injection angles such as 10°, 20° and 40° against the main flow direction. As the injection angle increases, two counter-balancing effects were observed.

A MEMS Singlet Oxygen Generator—Part II: Experimental Exploration of the Performance Space

This paper reports the quantitative experimental exploration of the performance space of a microfabricated singlet oxygen generator (muSOG). SOGs are multiphase reactors that mix H2O2, KOH, and Cl2 to produce singlet delta oxygen, or O2 (a). A scaled-down SOG is being developed as the pump source for a microfabricated chemical oxygen-iodine laser system because scaling down a SOG yields improved performance compared to the macroscaled versions. The performance of the muSOG was characterized using O2 (a) yield, chlorine utilization, power in the flow, molar flow rate per unit of reactor volume, and steady-state operation as metrics. The performance of the muSOG is measured through a series of optical diagnostics and mass spectrometry. The test rig, which enables the monitoring of temperatures, pressures, and the molar flow rate of O2 (a), is described in detail. Infrared spectra and mass spectrometry confirm the steady-state operation of the device. Experimental results reveal O2 (a) concentrations in excess of 1017 cm-3, O2 (a) yield at the chip outlet approaching 80%, and molar flow rates of 02(a) per unit of reactor volume exceeding 600 times 10-4 mol/L/s.

Numerical study of base effects on population inversion in DF chemical laser cavity

Nowadays a chemical laser is globally studied and examined as a means of new high strategic weapon system or industrial equipment system. Different from the other laser systems, the chemical laser system has a great advantage in that a high power laser beam with megawatt range can be easily generated. In order to do that, the chemical laser system employs a supersonic mixing and chemical reaction in the cavity. In the DF chemical laser system, F atom as an oxidant and D 2 molecule as a fuel are injected and reacted so that the DF excited molecules are produced. These phenomena occur in a non-equilibrium state. The excited molecules are degenerated into the lower level energy states so as to generate the laser beam by means of the stimulated emission. Therefore, more excited molecules in higher energy level are desirable in order to generate a higher power laser beam by controlling a flow mixing and chemical reaction in the cavity. There are a lot of factors that may affect mixing and chemical reaction in producing excited molecules. Usually, the chemical laser system adopts a diffusion type of injection system with base. Thereby, a recirculation zone is formed behind the base which determines characteristics of mixing and chemical reaction. In this study, the effects of base height on the population inversion, that is one of the most important aspects in the chemical laser system, are numerically investigated. The results are discussed by considering three base heights of 0.4, 0.8 and 1.6 mm. Major results reveal that a transition of DF(1)–DF(0) as one of population inversions takes place in the whole range of cavity while its value decreases as the base height increases. On the contrary, the region over which the transitions of DF(2)–DF(1) and DF(3)–DF(2) occur, increases as the base height increases, while so does its value. Therefore, as the base height decreases, the maximum small signal gain (SSG) becomes higher in the v 1–0 transition, whereas it becomes lower in the v 2–1, v 3–2 and v 4–3 transitions except in the nozzle inlet. Accordingly, the total extracted power is found to become higher with a decrease in base height.

Optical spectroscopic based in-line iodine flow measurement system – an application to COIL

Precision measurement of iodine concentration is an essential diagnostic tool in the development and optimization of chemical oxygen-iodine laser (COIL) system. A simple technique based on absorption spectroscopy has been developed and the absorption cell assembly was interfaced with the data acquisition and control system (DACS) for monitoring the iodine flow rate in real time. The assembly is being used in our 500 W COIL system and more than 600 power runs have been given.

중수소 분사각에 따른 불화중수소 화학레이저의 성능향상에 관한 수치적 연구

환형 노즐을 갖는 불화중수소 화학레이저 시스템에서 레이저빔 발진은 불소 원자와 중수소 분자의 혼합을 통해서 얻어진다. 초음속 연소기에서 연료의 분사각이 성능에 큰 영향을 미친다는 연구에 근거하여, 혼합률을 증진시키기 위한 연구로서 주유동과 일정각을 가지고 분사되는 중수소의 불소 원자와의 혼합률 증진에 대한 수치적 연구를 수행하였다. 중요 결과로서 중수소 분사각(10, 20, 40도)이 커짐에 따라서 최대 소신호 광학이득계수와 레이저 공동내의 압력이 상승하게 된다. 또한, 광학이득계수와 공동압력의 관점에서 불화중수소 화학레이저 발진을 위한 최대 성능은 20~40도 사이의 중수소 분사각에서 나타난다. In the chemical laser system with a radial expansion nozzle array, the laser beam generation is achieved by mixing F atom from supersonic nozzle and <TEX>$D_{2}$</TEX> molecule from holes of round-bended supply line. Based on that the fuel injection angle with main stream has a great influence of performance on supersonic combustor, the effects of <TEX>$D_{2}$</TEX> injection angles with the main F flow on mixing enhancement are numerically investigated. The results are discussed by comparison with three cases of <TEX>$D_{2}$</TEX> injection angles; <TEX>$10^{o}$</TEX>, <TEX>$20^{o}$</TEX> and <TEX>$40^{o}$</TEX> with the main flow direction. Major results reveal that as the <TEX>$D_{2}$</TEX> injection angle increases, the maximum small signal gains and the static pressure in the laser cavity become higher. Consequently, the <TEX>$D_{2}$</TEX> injection angle between <TEX>$20^{o}$</TEX> and <TEX>$40^{o}$</TEX> is recommended as an optimized geometric parameter in consideration of both of high gains and low cavity pressure.

Effects of pressure ratio on population inversion in a DF chemical laser with concurrent lasing

A numerical simulation is presented for investigating the effects of pressure ratio of D 2 injector to supersonic nozzle on the population inversion in the DF chemical laser cavity, while a lasing concurrently takes place. The chemical laser is generally used for the industrial process and manufacturing as well as the military weapon system, which requires high power characteristic of laser system rather than the others. The population inversion is absolutely needed to generate the laser beam and is non-equilibrium process. The laser beam is generated between the mirrors in the cavity and it is important to obtain stronger population inversion and more uniform distribution of the excited molecules in the laser cavity in order to produce high-power laser beam with good quality. In this study, these phenomena are investigated by means of analyzing the distributions of the DF excited molecules and the F atom used as an oxidant, while simultaneously estimating the maximum small signal and saturated gains and power in the DF chemical laser cavity. For the numerical solution, a fully conservative implicit method and a second order total variation diminishing (TVD) scheme are used with the finite-volume method (FVM). An 11-species (including DF molecules in various excited states of energies), 32-step chemistry model is adopted for the chemical reaction of the DF chemical laser system. The results are discussed by comparison with two D 2 injector pressure cases; 192 and 388.64 torr. Major results reveal that in the resonator, stronger population inversions occur in the all transitions except DF(1)-DF(0), when the D 2 injection pressure is lower. But, the higher D 2 injection pressure provides a favorable condition for DF(1)-DF(0) transition to generate the higher power laser beam. In other words, as the pressure of D 2 injector increases, the maximum small signal gain in the v 1 - 0 transition, which is in charge of generating most of laser power, becomes higher. Therefore, the total laser beam power becomes higher.

Measurement of the rate constant for the quenching of [formula omitted] by O 2(X) at 150 K

Electronic energy transfer between I atoms and O 2 molecules, O 2( a 1Δ) + I( 2 P 1 2 ) ↔ O 2( X 3 Σ −) + I( 2 P 1 2 ) , is a process of central importance in chemical oxygen-iodine laser (COIL) systems. Rate constants for the forward and reverse steps are well defined for room temperature. However, supersonic COIL devices operate with local gas temperatures near 150 K. To facilitate modeling of these lasers, the rate constant for quenching of I( 2 P 1 2 ) by O 2(X) has been measured at a temperature of 150 K. The result obtained, k b = (4.6 ± 1.0) × 10 −12 cm 3 s −1, is appreciably smaller than the values used in current computational models.

High-power stable chemical oxygen iodine laser

A high-power chemical oxygen iodine laser system has been developed with industrial applications in mind. The present system shows fairly high efficiency, good stability, and reasonably good beam quality applicable to practical applications. Highly efficient power transmission through optical fibers has been demonstrated.

Nature of the red emission in the chemical oxygen iodine laser system

Intense red emission peaking at 703 nm is observed when a heated metal wire is placed downstream of an O 2( 1Δ g) generator used in the chemical oxygen iodine laser (COIL) system. The O 2( 1Δ g) is produced by bubbling Cl 2 through an alkaline solution of H 2O 2. Evidence is presented that strong red emission requires the presence of both O 2( 1Δ g) and Cl 2 in contact with a heated metal surface. Several metals have been used. The red emission spectrum is independent of the metal and the intensity is strongest for copper.

Chemical laser systems analysis

This paper presents a means by which the chemical laser device weight can be minimized with respect to its performance and the device power minimized with respect to the target range. Chemical laser performance parameters such as the specific power and nozzle power flux are then used in conjunction with weight and propagation models to determine system effectiveness. A measure of merit is given by which systems can be contrasted. An illustrative example is included in which DF and Iodine laser systems are compared for an airborne scenario. 14 references.

Vibrational relaxation and electronic quenching rate coefficients for BiF(A0+,v′) by SF6

We have extended our kinetic data base for the A state of BiF to include SF6 as a collision partner. By applying a four level finite difference fitting routine to time-resolved fluorescence traces from v′=0–3, we have obtained rate coefficients for electronic quenching, and for vibrational relaxation within the A-state manifold. As was the case for our previous results in He and Ar, electronic quenching is slow in comparison to radiative decay. Vibrational relaxation does not show a simple v′ dependence, but rather, for the levels examined, increases markedly for higher v′. Our results confirm the suitability of SF6 as a bulk diluent in the proposed NF/BiF chemical laser system.

New singlet oxygen generator for chemical oxygen-iodine lasers

Experiments have been carried out to investigate a new method for generating O2(1Δ) with long-time operation of an efficient chemical oxygen-iodine laser system in mind. An impinging-jet nozzle was utilized to atomize a H2O2-KOH solution so that the alkaline H2O2/Cl2 reaction might occur in droplet-gas phase with high excitation efficiency. Experimental results indicate that the present generator can yield as high as 80% of O2(1Δ) with reasonable O2 flow rate.

Determination of gas concentrations and temperature in the exhaust of a power plant with a cw chemical HF laser

A cw chemical hydrogen fluoride laser system was used to investigate the exhaust of a gas and garbage burning power plant for the period of three months. The concentration of water vapor and carbon dioxide as well as the temperature in the exhaust was measured online with a time resolution as small as 5 ms. The temperature could be determined with a relative accuracy of better than 0.1 K over an averaging time of 9 s. This high accuracy together with the fast response make the system well suited not only for industrial combustion control but also for remote and precise measurement of temperature profiles.

Gaseous actinometry measurements in a flashlamp-pumped pulsed chemical laser

A method is described for applying the well-known technique of gaseous actinometry to determine the initial degree of fluorine dissociation in a flashlamp-pumped chemical laser system. The method is based on a model which takes into account multiple reflections and different path lengths for the incident light in a flashlamp-pumped chemical laser. The use of the method is illustrated with measurements made on a ∼2-liter pulsed chemical laser, and the results are compared with previously reported measurements using other techniques.

Iodine monofluoride B 3Π(0+)→X 1Σ+ lasing from collisionally pumped states

An optically pumped IF laser operating on the B 3Π(0+)→X 1Σ+ transition has been studied. Vibrational levels v′=1, 2, 3, 4, 5, and 6 of IF(B) were pumped by a dye laser pulse and lasing was observed both from the level pumped and from lower levels populated as a result of collisions with bath gas molecules. Time delays from 0.5 to 3.0 μs were observed between termination of the pump pulse on v′=5 and lasing out of v′=0. The longer delays result from slower vibrational relaxation at lower pressures. The stable nature of v′=0 reservoir indicates that the B–X electronic transition is very attractive as a potential chemical laser system.

Experimental investigation of the characteristics of a planar surface discharge

An investigation was made of the optical and electrical characteristics of a planar surface discharge suitable for use in lasers. The optimal times and discharge input energies were determined for which the efficiency of conversion of electrical energy into 240–340 nm ultraviolet radiation energy was 5.5, 3.5, and 1.25% respectively, for Xe:F2=10:1, Ar:F2=10:1, and He:F2=10:1 gas mixtures at atmospheric pressure. A chemical laser system was proposed employing initiation by a planar surface discharge. The possibility was investigated of increasing the fraction of ultraviolet radiation by forming excimer complexes of the type KrF* and XeCl* in the surface discharge plasma. For an HCl:Xe:Ar =1:1:30 gas mixture the surface-discharge optical radiation came predominantly from the excimer molecules when the specific input energy was < 5 mJ/cm2. The possibility was demonstrated of utilizing a surface discharge in excimer flashlamps of high repetition frequency (up to ~10 kHz) and emitting ultraviolet radiation of surface power density ~0.3 W/cm2.