Darren M. King

Continuous-wave laser oscillation on the 1315nm transition of atomic iodine pumped by O2(a1Δ) produced in an electric discharge

Laser action at 1315nm on the I(P1∕22)→I(P3∕22) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O2(a1Δ) which is produced using wet-solution chemistry. The difficulties in chemically producing O2(a1Δ) has motivated investigations into purely gas phase methods to produce O2(a1Δ) using low-pressure electric discharges. In this letter, we report on the demonstration of a continuous-wave laser on the 1315nm transition of atomic iodine where the O2(a1Δ) used to pump the iodine was produced by a radio-frequency-excited electric discharge. The electric discharge was sustained in a He∕O2 gas mixture upstream of a supersonic cavity which is employed to lower the temperature of the continuous gas flow and shift the equilibrium of atomic iodine in favor of the I(P1∕22) state. The laser output power was 220mW in a stable cavity composed of two 99.99% reflective mirrors.

Measurement of positive gain on the 1315nm transition of atomic iodine pumped by O2(a1Δ) produced in an electric discharge

Laser action at 1315nm on the I(P1∕22)→I(P3∕22) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O2(a1Δ), which is produced using wet-solution chemistry. The system difficulties of chemically producing O2(a1Δ) has motivated investigations into gas phase methods to produce O2(a1Δ) using low-pressure electric discharges. In this letter we report on positive gain on the 1315nm transition of atomic iodine where the O2(a1Δ) was produced in a flowing electric discharge. The electric discharge was followed by a continuously flowing supersonic cavity that was necessary to lower the temperature of the flow and shift the equilibrium of atomic iodine more in favor of the I(P1∕22) state. A tunable diode laser system capable of scanning the entire line shape of the (3,4) hyperfine transition of iodine provided the measurements of gain.

Path to the measurement of positive gain on the 1315-nm transition of atomic iodine pumped by O/sub 2/(a/sup 1//spl Delta/) produced in an electric discharge

Laser action at 1315 nm on the I(/sup 2/P/sub 1/2/)/spl rarr/I(/sup 2/P/sub 3/2/) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O/sub 2/(a/sup 1//spl Delta/) which is produced using wet-solution chemistry. The system difficulties of chemically producing O/sub 2/(a/sup 1//spl Delta/) have motivated investigations into gas phase methods to produce O/sub 2/(a/sup 1//spl Delta/) using low-pressure electric discharges. We report on the path that led to the measurement of positive gain on the 1315-nm transition of atomic iodine where the O/sub 2/(a/sup 1//spl Delta/) was produced in a flowing electric discharge. Atomic oxygen was found to play both positive and deleterious roles in this system, and as such the excess atomic oxygen was scavenged by NO/sub 2/ to minimize the deleterious effects. The discharge production of O/sub 2/(a/sup 1//spl Delta/) was enhanced by the addition of a small proportion of NO to lower the ionization threshold of the gas mixture. The electric discharge was upstream of a continuously flowing supersonic cavity, which was employed to lower the temperature of the flow and shift the equilibrium of atomic iodine more in favor of the I(/sup 2/P/sub 1/2/) state. A tunable diode laser system capable of scanning the entire line shape of the (3,4) hyperfine transition of iodine provided the gain measurements.

Continuous-wave laser oscillation in subsonic flow on the 1315nm atomic iodine transition pumped by electric discharge produced O2(aΔ1)

Herein the authors report on the demonstration of a continuous-wave laser in subsonic flow on the 1315nm transition of atomic iodine using the energy transferred to I(P1∕22) from O2(aΔ1) produced by a radio-frequency-excited electric discharge. The electric discharge was sustained in an O2–He–NO gas mixture. Downstream of the discharge, cold gas injection was employed to raise the gas density and lower the temperature of the continuous gas flow to shift the equilibrium of atomic iodine in favor of the I(P1∕22) state. The laser output power was 540mW in a stable cavity with two 99.993% reflective mirrors.

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.

RECENT EXPERIMENTAL MEASUREMENTS OF THE ELECTRICOIL SYSTEM

Theoretical and experimental studies have indicated that fractions of O 2 ( 1 Δ) can be produced in an electrical discharge that may permit lasing of an electric discharge oxygen-iodine laser (ElectriCOIL) system, possibly in conjunction with the injection of predissociated iodine. Results of those studies along with more recent experimental results show that electric excitation is a complex process that must be investigated with advanced diagnostics along with modeling to better understand this highly complex system. In this paper, recent detailed experimental measurements of the RF discharge region in the ElectriCOIL system are presented, including E/N and temperature measurements. Diagnostics play a critical role in developing an understanding of the ElectriCOIL system; and, as such, a great deal of care has been taken to implement high quality diagnostics for evaluating the flow properties emerging from the discharge region. Spectroscopic temperature measurements are taken from the O 2 ( 1 Σ) emission data.

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.

Studies of CW laser oscillation on the 1315-nm transition of atomic iodine pumped by O/sub 2/(a/sup 1//spl Delta/) produced in an electric discharge

In this paper, we report on studies of a continuous-wave laser at 1315 nm on the I(/sup 2/P/sub 1/2/)/spl rarr/I(/sup 2/P/sub 3/2/) transition of atomic iodine where the O/sub 2/(a/sup 1//spl Delta/) used to pump the iodine was produced by a radio frequency excited electric discharge. The electric discharge was sustained in He-O/sub 2/ and Ar-O/sub 2/ gas mixtures upstream of a supersonic cavity which is employed to lower the temperature of the continuous gas flow and shift the equilibrium of atomic iodine in favor of the I(/sup 2/P/sub 1/2/) state. The results of experimental studies for several different flow conditions, discharge arrangements, and mirror sets are presented. The highest laser output power obtained in these experiments was 520 mW in a stable cavity composed of two 99.995% reflective mirrors.

Superlinear Enhancement of Discharge Driven Electric Oxygen-Iodine Laser by Increasing

Continuing experiments with electric oxygen-iodine laser (ElectricOIL) technology have significantly increased laser power output by increasing the product of gain and gain-length, <i>g</i>₀<i>L</i>. The authors report on progress with recent ElectricOIL devices utilizing a new concentric discharge geometry with improved O₂(<i>a</i>¹Δ) production at higher discharge operating pressure at higher system flow rates. O₂(<i>a</i>¹Δ) produced in flowing radio-frequency discharge in O₂-He-NO gas mixture is used to pump <i>I</i>(²<i>P</i>_1/2) by near-resonant energy transfer, and laser power is extracted on the <i>I</i>(²<i>P</i>_1/2)→ <i>I</i>(²<i>P</i>_3/2) transition at 1315 nm. Advancements in heat exchanger design reduce O₂(<i>a</i>¹Δ) wall loss without sacrificing significant cooling efficiency improving best gain performance from 0.26 to 0.30% cm^-1. Modeling of recent data is presented. By increasing the gain length (system size) by a factor of 3, a 5-fold increase in laser output on the 1315-nm transition of atomic iodine was achieved. Flow conditions with <i>g</i>₀<i>L</i> = 0.042 were used to extract a continuous wave average total laser power of 481 W. A low frequency ±11.9% oscillation in the total power was observed giving a peak outcoupled power of 538 W.

g_{0}{L}

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.