D. Furman

Diode-laser-based absorption spectroscopy diagnostics of a jet-type O/sub 2/(/sup 1//spl Delta/) generator for chemical oxygen-iodine lasers

Using diode-laser-based diagnostics, O/sub 2/(/sup 1//spl Delta/) yield and water vapor fraction were measured at the exit of a jet-type singlet oxygen generator (JSOG) for a chemical oxygen-iodine laser (COIL). Chlorine utilization and gas temperature at the generator exit were also measured, simultaneously. For conditions corresponding to the maximum chemical efficiency of the supersonic COIL energized by the JSOG, the O/sub 2/(/sup 1//spl Delta/) yield, water vapor fraction, chlorine utilization, and temperature at the generator exit are 0.65, 0.08 and 0.92, and 30/spl deg/C, respectively. Increase of the basic hydrogen peroxide temperature results in an increase of the water vapor fraction caused by an increase of the saturated water vapor pressure in the generator. As the pressure in the generator rises from 18 to 60 torr, the yield decreases from 0.65 to O.48. Dependence of the yield on the generator pressure is consistent with a rate constant for the O/sub 2/(/sup 1//spl Delta/) energy pooling reaction of 2.7/spl times/10/sup -17/ cm/sup 3//spl middot/S/sup -1/. The same rate constant explains the measured variation of the temperature along the flow in the diagnostic cell.

Parametric study of small-signal gain in a slit nozzle, supersonic chemical 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 O/sub 2/(/sup 1//spl Delta/) molecules lost in the region of iodine dissociation per I/sub 2/ molecule.

Power optimization of small-scale chemical oxygen-iodine laser with jet-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 Cl/sub 2/ 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/sup -1/. 190 W and 10.5% were obtained for 20 mmol/s of CI/sub 2/ flow rate. Replacing He by N/sub 2/ 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.

An efficient supersonic chemical oxygen–iodine laser operating without buffer gas and with simple nozzle geometry

We report on an efficient supersonic chemical oxygen-iodine laser, energized by a jet-type singlet oxygen generator, operating without primary buffer gas and applying simple nozzle geometry and transonic mixing of iodine and oxygen. Output power of 177 W with chemical efficiency of 17% was obtained in a 5 cm gain length for Cl2 flow rate of 11 mmol/s. The power is almost unaffected by water vapor in the medium.

Analysis of lasing in gas-flow lasers with stable resonators

A model is developed that describes the power extraction in chemical oxygen-iodine lasers (COILs) and CO(2) gasdynamic lasers with stable resonators when a large number of transverse Hermite-Gaussian eigenmodes oscillate. The extraction efficiency, mode intensities, and intensity distribution along the flow depend only on two parameters. The first is the ratio gamma(0) of the residence time of the gas in the resonator to the O(2)((1)D) or N(2)(v) energy extraction time and the second is the ratio of the threshold to the small-signal gain. The efficiency is maximum for gamma(0) ? infinity and decreases rapidly as gamma(0) decreases. It is found that for a range of parameters corresponding to the highest efficiencies the intensity distribution along the flow is nonuniform and has two peaks near the upstream and downstream sections of the resonator. In this case only the highest-order modes that totally fill the resonator cross section oscillate (the so-called, experimentally observed sugar scooping bimodal intensity distribution). For the range of parameters corresponding to smaller efficiencies the intensity is uniform. In this case all the modes participate in lasing; however, the intensities of the high-order modes are larger than those of the low order. The current model is compared with the plane-mirror Fabry-Perot resonator model and with the constant intraresonator intensity and rooftop models of COILs with stable resonators. The extraction efficiency calculated with the last two models is close to that estimated from our model. However, the intensity distribution cannot be calculated correctly using the Fabry-Perot, the constant intraresonator intensity, or the rooftop model.

Spatial distribution of the gain and temperature across the flow in a slit-nozzle supersonic chemical oxygen-iodine laser with transonic and supersonic schemes of iodine injection

Spatial distributions of the gain and temperature across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit-nozzle supersonic chemical oxygen-iodine laser as a function of the iodine and secondary nitrogen flow rate, jet penetration parameter, and gas pumping rate. The mixing efficiency for supersonic injection of iodine (/spl sim/0.85) is much larger than for transonic injection (/spl sim/0.5), the maximum values of the gain being /spl sim/0.65%/cm for both injection schemes. Measurements of the gain distribution as a function of the iodine molar flow rate nI/sub 2/ were carried out. For transonic injection, the optimal value of nI/sub 2/ at the now centerline is smaller than that at off axis locations. The temperature is distributed homogeneously across the flow, increasing only in the narrow boundary layers near the walls. Opening a leak downstream of the cavity in order to decrease the Mach number results in a much larger mixing efficiency (/spl sim/0.8) than for a closed leak.

Parametric study of an efficient supersonic chemical oxygen-iodine laser/jet generator system operating without buffer gas

A detailed experimental study of an efficient supersonic chemical oxygen-iodine laser is presented. The laser is energized by a jet-type singlet oxygen generator, operated without primary buffer gas and applies simple nozzle geometry and transonic mixing of iodine and oxygen. Output power of 190 W with chemical efficiency of 18% was obtained in a 5-cm gain length for Cl/sub 2/ flow rate of 11.8 mmole/s. The power is studied as a function of the distance between the optical axis and the supersonic nozzle exit plane, the molar flow rates of various reagents, the basic hydrogen peroxide solution and gas pressures in the generator, the type of the secondary buffer gas (N/sub 2/ or He) and the stagnation temperature of the gas. It is found that the power under the present operation conditions is almost unaffected by water vapor in the medium. The role of buffer gas under different conditions is discussed.

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

A simple 1-D model is developed for the fluid dynamics and chemical kinetics in the chemical oxygen iodine laser (COIL). Two different I/sub 2/ 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 Heavens dissociation mechanism is much lower than the measured one. Employing Heidners 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.

Gain and Temperature in a Slit Nozzle Supersonic Chemical Oxygen-Iodine Laser with Transonic and Supersonic Injection of Iodine

Spatial distributions of the gain and temperament across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser as a function of the iodine and secondary nitrogen flow rate, jet penetration parameter and gas pumping rate. The mixing efficiency for supersonic injection of iodine is found to be much larger than for transonic injection, the maximum values of the gain being approximately 0.65 percent/cm for both injection schemes. Measurements of the gain distribution as a function of the iodine molar flow rate nI2 were carried out. For transonic injection the optimal value of nI2 at the flow centerline is smaller than that at the off axis location. The temperature is distributed homogeneously across the flow, increasing only in the narrow boundary layers near the walls. Opening a leak downstream of the cavity in order to decease the Mach number results in a decrease of the gain and increase of the temperature. The mixing efficiency in this case is much larger than for closed leak.

Mechanisms of COIL operation: experiment and modeling

Spatial distributions of the gain, temperature and I2 across the flow were studied for transonic and supersonic schemes of the iodine injection in a slit nozzle supersonic chemical oxygen-iodine laser (COIL) as a function of the iodine and secondary nitrogen flow rate and jet penetration parameter. The mixing efficiency for supersonic injection of iodine (~ 0.85) is found to be much larger than for transonic injection (~ 0.5), the maximum values of the gain being ~ 0.65%/cm for both injection schemes. Spatial distributions of the gain corresponding to the maximum power are found. A simple one-dimensional model is developed for the fluid dynamics and chemical kinetics in the COIL. Two different I2 dissociation mechanisms are tested against the performance of a COIL device in our laboratory. The two mechanisms chosen are the celebrated mechanism of Heidner and the newly suggested mechanism of Heaven. 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 flow parameters.