Gabriel F. Benavides

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.

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.

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.

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.

UltraSail - Ultra-Lightweight Solar Sail Concept

UltraSail is a next-generation high-risk, high-payoff sail system for the launch, deployment, stabilization and control of very large (sq km class) solar sails enabling high payload mass fractions for high (Delta)V. Ultrasail is an innovative, non-traditional approach to propulsion technology achieved by combining propulsion and control systems developed for formation-flying micro-satellites with an innovative solar sail architecture to achieve controllable sail areas approaching 1 sq km, sail subsystem area densities approaching 1 g/sq m, and thrust levels many times those of ion thrusters used for comparable deep space missions. Ultrasail can achieve outer planetary rendezvous, a deep space capability now reserved for high-mass nuclear and chemical systems. One of the primary innovations is the near-elimination of sail supporting structures by attaching each blade tip to a formation-flying micro-satellite which deploys the sail, and then articulates the sail to provide attitude control, including spin stabilization and precession of the spin axis. These tip micro-satellites are controlled by 3-axis micro-thruster propulsion and an on-board metrology system. It is shown that an optimum spin rate exists which maximizes payload mass.

Gain and continuous-wave laser power enhancement with a multiple discharge electric oxygen-iodine laser

Herein the authors report on the demonstration of a 70% enhancement in gain and 98% enhancement in continuous-wave laser power on the 1315nm transition of atomic iodine via an increase in flow rates and pressure using multiple discharges in an electric oxygen-iodine laser. O2(aΔ1) is produced by two parallel radio-frequency-excited electric discharges sustained in an O2–He–NO gas mixture, a secondary discharge predissociated the molecular iodine, and I(P1∕22) is then pumped using energy transferred from O2(aΔ1). A gain of 0.17%cm−1 was obtained and the total laser output power was 12.3W.

Gain recovery in an electric oxygen-iodine laser

Recent investigations of an electric oxygen-iodine laser system have shown that computational modeling overpredicts the experimentally measured power output for similar gain conditions. This discrepancy is potentially due to an unknown reaction that competes with the forward pumping of I(P21/2) by O2(a Δ1). Measurements of gain recovery downstream of an operating laser cavity were performed. Modeling of this experiment shows that reducing the forward pumping rate by an effective factor of approximately 4 to simulate a competing mechanism results in the computational modeling matching the experimental gain recovery measurements, and in improved agreement between the measured and modeled laser power extraction.

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.

Deployment Experiment for Ultralarge Solar Sail System (UltraSail)

UltraSail is a next-generation high-payoff system with very large (kilometers-squared class) solar sails enabling high payload mass fractions for high Delta-V. One of the primary innovations is the near elimination of sail supporting structures by attaching each blade tip to a formation-flying tip satellite. To design the deployment of kilometers-long blades by centrifugal force provided by tip satellites, the peel force of the blade material must be known. In this research, an experiment to determine the force necessary to deploy a stowed film in a vacuum was designed, fabricated, and operated for various CP-1 polyimide film samples, including uncoated, aluminum-coated, and uncoated but conductive film. Results for uncoated film samples were heavily dependent on vacuum levels, with very high forces observed at low pressures due to electrostatic charge buildup. However, for the coated film and conductive film samples, the types most likely to be used on an UltraSail mission, preliminary results show that the peel forces are negligibly small. This small peel force is critical for the successful, simple, and efficient deployment of the UltraSail system. A potential problem associated with trapped air between film layers was identified by the experiment, and a future winding scheme will guard against this issue.

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.