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

Laser action at 1315 nm on the I(²P₁2/)→I(²P₃2/) 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) have motivated investigations into gas phase methods to produce O₂(a¹Δ) 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 O₂(a¹Δ) 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 O₂(a¹Δ) 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(²P₁2/) 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.