Path to the measurement of positive gain on the 1315-nm transition of atomic iodine pumped by O2 (a1 Δ) produced in an electric discharge

Laser action at 1315 nm on the I(P-2(1/2)) --> I(P-2(3/2)) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O-2 (alpha(1)Delta) which is produced using wet-solution chemistry. The system difficulties of chemically producing O-2(alpha(1)Delta) have motivated investigations into gas phase methods to produce O-2(alpha(1)Delta) using low-pressure electric discharges. In this paper, we report on the path that led to the measurement of positive gain on the 1315-nm transition of atomic iodine where the O-2(alpha(1)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 NO2 to minimize the deleterious effects. The discharge production of O-2(alpha(1)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(P-2(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.