Magnetic modulation of gain in a chemical oxygen-iodine laser

A magnetic modulation of gain in a continuous-wave (CW) chemical oxygen-iodine laser (COIL) is proposed for several regimes of laser generation. The principle of the method proposed is based on a direct magnetic modulation of gain in the active zone of a COIL utilizing the Zeeman effect on the laser transition ²P_1/2 -²P_3/2 of iodine atoms. The possible applications of this technique to control the laser generation in COIL for technological purposes are outlined     

连续波化学氧碘激光器的小信号增益和腔内损耗

本文用变耦合率方法和平行板转动最大损耗法分别测出小信号增益为1.60×10~(-3)cm~(-1)和1.75×10~(-3)cm~(-1),腔内损耗为12.0％,获得了饱和参量为3.00kw/cm~2,并将所得结果与其它报道作了比较。     

Parametric study of the gain in a small scale, grid nozzle,supersonic chemical oxygen-iodine laser

We report on experiments and model calculations of the small-signal gain and the gain profile in a grid nozzle supersonic chemical oxygen-iodine laser. The laser has a 5-cm long active medium and the gain is measured using a diode laser. The calculations are based on a simple one-dimensional semiempirical model previously developed in our laboratory. The gain is studied as a function of the molar flow rates of the various reagents and optimal conditions are found for maximum gain. In particular, an optimal value of the flow rate of I₂ is found in the experiment and explained by the present model. The small size and the simple structure of the laser combined with the simplicity of the model make the present system a useful tool for studying parameters important for high power supersonic iodine lasers     

A simplified analytic model for gain saturation and powerextraction in the flowing chemical oxygen-iodine laser

This paper describes the development of a simplified saturation model (SSM) for predicting power extraction from a chemical oxygen-iodine laser (COIL). Using the Fabry-Perot gain saturation assumption, analytic expressions for COIL extraction efficiency are presented for both constant-density and variable-density cavity conditions. The model treats mirror scattering, nonsaturable distributed losses, and diffractive losses from the mode-limiting aperture and is shown to be in excellent agreement with experimental COIL power extraction data. A comparison of the model with the Rigrod power extraction model is presented showing that the Rigrod model accurately predicts COIL extraction efficiency only in the limit that the COIL device no longer behaves as a transfer laser     

电引发脉冲氧碘化学激光器的增益

本文对脉冲氧碘化学激光器的增益性能进行了理论估算。碘原子由CH_3I电离产生。研究了各种压力条件下成份比和CH_3I离解度对增益系数的影响。     

One-dimensional modeling of the gain and temperature in asupersonic chemical oxygen-iodine laser with transonic injection ofiodine

A simple 1-D model is developed for the fluid dynamics and chemical kinetics in the chemical oxygen iodine laser (COIL). Two different I₂ dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two dissociation mechanisms chosen are the celebrated mechanism of Heidner (1983) and the newly suggested mechanism of Heaven (2001). The gain calculated using Heaven's dissociation mechanism is much lower than the measured one. Employing Heidner's mechanism, a surprisingly good agreement is obtained between the measured and calculated gain and temperature over a wide range of the flow parameters. Other predictions of the model (larger mixing efficiency and higher temperature with a leak opened downstream of the resonator and gain decrease along the flow) are also in agreement with the experimental observations     

氧碘化学激光束特性的检测

在氧碘化学激光器上测试激光束的特性,为进一步研究该激光器的“化学问题”和“光学问题”提供了一定的依据。     

脉冲氧碘化学激光放大器的理论模型

本文提出脉冲氧碘化学激光主振荡器加功率放大器(MOPA)系统中放大器的理论模型。计算表明:氧碘放大器内采用折迭光路方案,可以获得高的放大率及化学效率。     

Small-signal gain and saturation parameter of a transverse-flow CW oxygen-iodine laser

The small-signal gain and saturation parameter of a transverse-flow CW oxygen-iodine laser have been experimentally obtained for the first time from output power measurements made as a function of the cavity losses without using a CW probe laser. These measurements typically yieldalpha_{0} simeq 0.045m^-1andI_{s} simeq 0.44kW/cm²for a Cl2flow rate of1.4 times 10^{-3}mol/s with an I2flow rate of4 times 10^{-6}mol/s. The dependences of the small-signal gain and saturation parameter have been also found on the Cl2flow rate. These behaviors are qualitatively explained by a simple two-level model.     

Performance of a high-efficiency 5-cm gain length supersonicchemical oxygen-iodine laser

The Air Force Phillips Laboratory has developed a small-scale supersonic chemical oxygen-iodine laser (COIL) test stand (VertiCOIL) to rapidly evaluate emerging potential technology improvements. VertiCOIL was designed to address issues relevant to military and commercial applications such as long run time, high-efficiency operation, and compact design. VertiCOIL demonstrated an overall chemical efficiency of nearly 27%, one of the highest chemical efficiencies ever achieved by a COIL. In addition, VertiCOIL was able to lase for greater than 1 h by employing a continuously cooled basic hydrogen peroxide (BHP) flowing loop. Measured resonator parameters were used with a simplified saturation model to calculate the optical extraction efficiency. The peak optical extraction efficiency predicted by the model was 0.82. The dependence of the predicted extraction efficiency on outcoupling fraction is in good agreement with experimental results. Combining the predicted extraction efficiency with the COIL heuristic equation results in good agreement between measured and predicted overall device chemical efficiency     

High-performance chemical oxygen-iodine laser using nitrogendiluent for commercial applications

A chemical oxygen-iodine laser (COIL), the VertiCOIL device, was transferred from the Air Force Research Laboratory (AFRL) to the University of Illinois at Urbana-Champaign (UIUC) and made operational. The performance of the high-power VertiCOIL laser was measured with nitrogen diluent, New nozzle designs were investigated and implemented to optimize nitrogen performance, Nitrogen diluent chemical efficiencies of 23% were achieved; these are the highest reported chemical efficiencies with room-temperature nitrogen diluent. A long duration, high chemical efficiency test was demonstrated with nitrogen diluent; a chemical efficiency of 18.545 at 30 mmol/s of chlorine was maintained for 35 min. The highest performance was obtained with new iodine injector blocks and a larger throat height. The new iodine injector blocks moved the injectors closer to the throat by 0.7 cm and the throat height was increased from 0.897 to 1.151 cm (0.353 to 0.453 in). The performance enhancements were in qualitative agreement with the system design predictions of the Blaze II chemical laser model. Three-dimensional computational fluid dynamics calculations using the general aerodynamic simulation program code confirmed the principle design change of moving the iodine injectors closer to throat     

Mode locking of a CW supersonic chemical oxygen-iodine laser

This paper presents the results of the first mode-locking experiments on a supersonic chemical oxygen-iodine laser (COIL). Mode locking has been achieved using an acoustooptic modulator (AOM) and lasing demonstrated on the TEM₀₀ modes with a small intracavity aperture. A dc magnetic field was used to increase the number of axial modes and a peak power of 2.5 kW has been reached with a pulse width of 2.1 ns at a repetition rate of 43.68 MHz     

Supersonic chemical oxygen-iodine laser with X-shaped streamwise vortex Generator

High-throughput operation of a supersonic chemical oxygen-iodine laser (COIL) is achieved with an advanced mixing nozzle. The mixing nozzle consists of a staggered arrangement of thin wedges lying across the flow duct, and looks like the letter "X" when it is viewed from the side. A 32.9% chemical efficiency is measured experimentally with this nozzle and buffer-gas precooling. Computational fluid dynamics (CFD) calculations are conducted to understand the rapid mixing capability of the nozzle. A series of streamwise vortices generated by the alternating wedges greatly enhances the mixing process in the supersonic stream and the rapid formation of the gain medium. The temperature and Mach number of the flow field are estimated from the gain-profile measurement of the I (/sup 2/P/sub 1/2/) to I (/sup 2/P/sub 3/2/) transition. Good agreement with the CFD calculations is seen.     

High-efficiency operation of chemical oxygen-iodine laser usingnitrogen as buffer gas

High-efficiency operation of supersonic chemical oxygen-iodine laser (COIL) with an advanced jet-type singlet oxygen generator using nitrogen as buffer gas was demonstrated. Laser output was remarkably increased when buffer gas was cooled with liquid nitrogen. The effects of buffer gas temperature on the characteristics of the oxygen-iodine laser medium was discussed. A net chemical efficiency of 23.4% was obtained at 405 W when the chlorine molar flow rate was 19 mmol/s     

放电引发脉冲氧碘化学激光器的研究

报道首次利用放电引发方法实现脉冲氧碘化学激光器的研究结果.证实低能电子也能很有效地引发氧碘激光反应.在O_2(~1(?))-CH_3I-N_2体系下激光能量输出达130mJ,电效率比光解方法高350倍.     

化学法生成碘原子应用于氧碘化学激光器的理论模拟

分析了化学法生成碘原子应用于COIL的优缺点,根据化学法生成碘原子的反应体系和氧碘化学激光器的反应机理建立了一维气体流动预混理论模型,从理论上研究了ClO2与NO反应生成Cl原子的产率随反应器压力的变化,加入HI的位置对生成I原子的影响,化学法生成碘原子代替碘分子注入到COIL中的小信号增益沿气流方向的变化,并与加入碘分子时进行了对比.     

Power optimization of small-scale chemical oxygen-iodine laser withjet-type singlet oxygen generator

Studies of power optimization of a 5-cm gain length chemical oxygen-iodine laser (COIL) energized by a jet-type singlet oxygen generator (JSOG) are presented. For 10 mmol/s of Cl₂ flow rate, output power of 132 W with chemical efficiency of 14.5% was obtained without a water vapor trap, 163 W and 18% were achieved when coholed (173 K). He was introduced downstream of the JSOG; under these conditions, the small-signal gain was estimated to be 0.32% cm^-1 . 190 W and 10.5% were obtained for 20 mmol/s of CI₂ flow rate. Replacing He by N₂ as a buffer gas resulted in a 13% power decrease only. The main key for increasing the chemical efficiency of a COIL without a water vapor trap for a given iodine-oxygen mixing system is found to be high oxygen pressure and low water vapor pressure inside the reaction zone of the JSOG. The last goal was achieved by optimizing the composition and temperature of the basic hydrogen-peroxide solution (BHP). The experimental results are discussed and related to the composition and flow conditions of the gaseous reactants and of the BHP     

Parametric study of small-signal gain in a slit nozzle, supersonicchemical oxygen-iodine laser operating without primary buffer gas

A detailed experimental study of the gain and temperature in the cavity of a supersonic chemical oxygen-iodine laser (COIL) is carried out to find optimal values of the flow parameters corresponding to the maximum gain. It is found that high gain (>0.7%/cm) can be obtained in a COIL operating without primary buffer gas and, hence, having a high gas temperature (>250 K) in the cavity. The measurements are performed for slit nozzles with different numbers and positions of iodine injection holes. Using a diode laser-based diagnostic, the gain is studied as a function of the molar flow rates of various reagents, with optical axis position along and across the flow, and Mach number in the cavity. Maximum gain of 0.73%/cm is obtained at chlorine and secondary nitrogen flow rates of 15 mmole/s and 7 mmole/s, respectively, for a slit nozzle with transonic injection of iodine. The gain is found to be strongly inhomogeneous across the flow. For a slit nozzle with iodine injection in the diverging part of the nozzle, the values of the maximum gain are smaller than for nozzles with transonic injection. Opening a leak downstream of the cavity in order to decrease the Mach number and increase the cavity pressure results in a decrease of the gain and dissociation fraction. The gain is a nonmonotonic function of the iodine flow rate, whereas the temperature increases with increasing iodine flow. An analytical model is developed for calculating in slit nozzles the iodine dissociation fraction F and the number N of O₂ (¹Δ) molecules lost in the region of iodine dissociation per I₂ molecule     

Measurements of peak power enhancement and power conservation inmagnetically gain-modulated chemical oxygen-iodine laser

A periodically pulsed regime of the magnetically gain-switched chemical oxygen iodine laser was investigated. The effects of different magnetic field intensity and pulse length on the laser power pulse enhancement and the mean power conservation were studied experimentally     

高增益激光的饱和效应和最佳输出耦合

本文在均匀和非均匀谱线加宽情况下,计算了高增益介质在不同小信号增益系数和吸收系数下的激光输出特性,并讨论了饱和效应和最佳输出耦合。