ABSTRACT
The chemical oxygen iodine laser (COIL) [1] is the only known example of a high-power chemically-driven electronic transition laser. Unlike other chemical lasers (e.g. HF/DF lasers described in section B3.4.2), which operate on rotational-vibrational transitions of molecules, the COIL operates on an atomic electronic transition. At present the COIL is the shortest wavelength chemical laser system [2, 3]. Figure B3.4.1.1 shows the electronic states of the species participating in the pumping process of the COIL. The laser transition, at 1315 nm, takes place between the spin-orbit levels of the ground state configuration of the iodine atom, I(5p5 2P1/2) → I(5p5 2P3/2). Basic chemical reactions taking place in the COIL are presented in table B3.4.1.1 [4, 5]. The iodine atoms are pumped by a near-resonant energy transfer from oxygen molecules in the excited singlet-delta state, O2(a 1g) (reaction 1, table B3.4.1.1). O2(1) is a metastable molecule with a very long radiative lifetime (76 min) [6] and a pronounced stability against collisional deactivation processes in many environments. Hence it can be used as the energy carrier for the COIL. Mixing of chemically produced O2(1) with I2 molecules results in dissociation of molecular iodine to atomic iodine which is subsequently excited via reaction 1 (table B3.4.1.1).
