David L. Carroll

Chemical laser modeling with genetic algorithms

A genetic algorithm technique was implemented to determine a set of unknown parameters that best matched the Blaze II chemical laser model predictions with experimental data. This is the first known application of the genetic algorithm technique for modeling lasers, chemically reacting flows, and chemical lasers. Overall, the genetic algorithm technique worked exceptionally well for this chemical laser modeling problem in a cost effective and time efficient manner. Blaze II was baselined to existing chemical oxygen-iodine laser data taken with the research assessment and device improvement chemical laser device with very good agreement. Mixing calculations for the research assessment and device improvement chemical laser nozzle indicate that higher iodine flow rates are necessary to maintain a significant fraction of the nominal performance as the total pressure is increased by the addition of helium ; this agrees with research assessment and device improvement chemical laser experimental data. It may be possible to implement this genetic algorithm technique to optimize the performance of any chemical laser as a function of any of the flow rates, mirror location, mirror size, nozzle configuration, injector sizes, and other factors. This modeling procedure can be used as a method to guide experiments to improve chemical laser performance.

Gain and continuous-wave laser power enhancement with a secondary discharge to predissociate molecular iodine in an electric oxygen-iodine laser

Herein the authors report on the demonstration of a 50% enhancement in gain and 38% enhancement in continuous-wave laser power on the 1315nm transition of atomic iodine through the addition of a secondary discharge to predissociate the molecular iodine in an electric oxygen-iodine laser. In the primary discharge the O2(aΔ1) is produced by a radio-frequency-excited electric discharge sustained in an O2–He–NO gas mixture, and I(P1∕22) is then pumped using energy transferred from O2(aΔ1). A gain of 0.10%cm−1 was obtained and the total laser output power was 6.2W.

Modeling of the ElectriCOIL system

Theoretical studies have indicated that sufficient fractions of O/sub 2/(/sup 1//spl Delta/) may be produced in an electrical discharge that will permit lasing of an electric discharge oxygen-iodine laser (ElectriCOIL) system. Results of those studies along with more recent experimental results show that electric excitation is a very complicated process that must be investigated with advanced diagnostics along with modeling to better understand this highly complex system. A kinetic package appropriate for the ElectriCOIL system is presented and implemented in the detailed electrodynamic GlobalKin model and the Blaze II chemical laser modeling code. A parametric study with the Blaze II model establishes that it may be possible to attain positive gain in the ElectriCOIL system, perhaps even with subsonic flow. The Blaze II model is in reasonable agreement with early gain data. Temperature is a critical issue, especially in the subsonic cases, and thus it appears that supersonic flow will be important for the ElectriCOIL system. Simulations of a supersonic ElectriCOIL system indicate that it may be possible to attain reasonable performance levels, even at low yield levels of 20% or less. In addition, pre-dissociation of the iodine is shown to be very important for the supersonic flow situation.

Mixing effects in postdischarge modeling of electric discharge oxygen-iodine laser experiments

In an electric discharge oxygen-iodine laser, laser action at 1315nm on the I(P1∕22)→I(P3∕22) transition of atomic iodine is obtained by a near resonant energy transfer from O2(aΔ1) which is produced using a low-pressure electric discharge. The discharge production of atomic oxygen, ozone, and other excited species adds higher levels of complexity to the postdischarge kinetics which are not encountered in a classic purely chemical O2(aΔ1) generation system. Mixing effects are also present. In this paper we present postdischarge modeling results obtained using a modified version of the BLAZE-II gas laser code. A 28 species, 105 reaction chemical kinetic reaction set for the postdischarge kinetics is presented. Calculations were performed to ascertain the impact of a two stream mixing mechanism on the numerical model and to study gain as a function of reactant mass flow rates. The calculations were compared with experimental data. Agreement with experimental data was improved with the addition of new kineti...

High-performance chemical oxygen-iodine laser using nitrogen diluent 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.

ElectriCOIL: an advanced chemical iodine laser concept

Advanced chemical iodine laser technology will logically include novel all gas phase generation techniques for an iodine energy donor and the injection of atomic rather than molecular iodine. Candidate methods are discussed for the creation of an all gas phase energy donor as well as for injecting atomic iodine. This research will lead directly to designs that will be fabricated and tested extensively with detailed diagnostics to evaluate the chosen designs performance attributes. Preliminary analysis and modeling of the ElectriCOlL system concept is presented. ElectriCOIL will reduce weight and simplify both military and commercial chemical iodine laser systems. Potential cost and weight savings are also envisioned as the massive quantities of liquid chemicals will be completely eliminated from the device operation.

Experimental study of cutting thick aluminum and steel with a chemical oxygen–iodine laser using an N2 or O2 gas assist

A chemical oxygen–iodine laser (COIL) was used to cut aluminum and carbon steel. Cut depths of 20 mm in aluminum and 41 mm in carbon steel were obtained using an N2 gas assist and 5–6 kW of power on target. The same laser at the same power level produced a cut depth of 65 mm in carbon steel with an O2 gas assist; a low quality cut to a depth of nearly 100 mm in carbon steel was also demonstrated. These data are compared with existing COIL and CO2 laser cutting data. COIL cuts carbon steel and stainless steel at approximately the same rate. For a given cut depth, power and spot size, COIL cuts steel approximately three times faster than a CO2 laser using an inert gas assist. COIL cutting speeds in carbon steel are improved by approximately a factor of three when an O2 assist is used in lieu of an N2 gas assist. With an N2 gas assist, COIL cuts aluminum at approximately the same rate as CO2 cuts steel. To improve the agreement between data and an existing theoretical cutting model, an empirical correction f...

Experimental study of continuous wave hydrogen-fluoride chemical laser overtone performance

The overtone lasing performance of the supersonic continuous wave hydrogen-fluoride chemical laser at the University of Illinois at Urbana-Champaign was optimized by the same set of flow rates that optimized the fundamental performance. When the absorption/scattering losses of the mirrors were taken into account, an overtone efficiency (the ratio of overtone power to maximum fundamental power for the same flow conditions) of 70-90% was achieved. The overtone efficiency was a strong function of medium saturation. There was no significant change in overtone power and efficiency as the mode volume increased. However, there was an increase in the number of lasing lines and a shift to higher rotational (J) lines. Overtone performance was as sensitive to cavitypressure as fundamental performance was

Diagnostic development for the ElectriCOIL flow system

Detailed studies of mechanisms for producing electrically initiated COIL lasers were previously presented. Results of those studies along with more recent experimental results show that electric excitation is a very complex process that must be investigated with advanced diagnostics. Theoretical studies indicate that fractions of O2(1(Delta) ) may be produced in the discharge that will permit lasing of an ElectriCOIL system. Recent kinetic studies indicate a range of useful operating parameters for ElectriCOIL that are analogous to those achieved in the all-chemical device. This can be accomplished at E/Ns in the range of 10-16 Volt-cm2. An experimental test bed has been built up to allow detailed diagnostic measurements of the discharge efficiencies and other experimental parameters. Results of early experiments are presented.

Measurements of Improved ElectricOIL Performance, Gain, and Laser Power

Ongoing experiments have led to continued improvements in the Electric Oxygen-Iodine Laser (ElectricOIL) system that significantly increased the performance, gain, and laser power output. Experimental investigations utilize radio-frequency discharges in O2/He/NO mixtures in the pressure range of 30-60 Torr. The goal of these investigations was maximization of both the yield and flow rate (power flux) of O2(aΔ) in order to produce favorable conditions for subsequent gain and lasing in our ElectricOIL system. Numerous measurements of O2(aΔ), oxygen atoms, and discharge excited states are made to characterize the discharge. A gain of 0.22% cm was measured with a corresponding outcoupled power of 28 W. Modeling with the BLAZE-IV model is in good agreement with data and helps to guide our understanding of this complex hybrid laser system.