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Improving the chemical efficiency of the supersonic chemical oxygen-iodine laser (COIL) is a key issue for the design of devices for both defense and industrial applications. Efficiencies around 30% for the supersonic COIL have been the state of the art in the last decade. Here, we report the achievement of a record (40%) for the chemical efficiency of the supersonic COIL. More specifically, we show that by carefully studying and optimizing the operation of the chemical generator, the mixing of heavy and light molecules in the gas phase and the optical extraction efficiency, we have approached the theoretical limit for the chemical efficiency.

We report on a highly efficient supersonic chemical oxygen–iodine laser (COIL), with supersonic mixing of iodine and oxygen. Output power exceeding 0.5 kW with chemical efficiency of ∼33% was obtained in a 5-cm gain length for Cl2 flow rate of 17 mmole/s. A 33% efficiency is the highest reported chemical efficiency of any supersonic COIL. Comparison between different mixing schemes shows that, for supersonic mixing, the output power and chemical efficiency are about 20% higher than for transonic mixing scheme. The optimal conditions for the efficient operation are investigated.

The gain and power in a supersonic chemical oxygen-iodine laser (COIL) are enhanced by applying dc corona/glow discharge in the transonic section of the secondary flow in the supersonic nozzle, dissociating I2 prior to its mixing with O2(Δ1). The loss of O2(Δ1) consumed for dissociation is thus reduced, and the consequent dissociation rate downstream of the discharge increases, resulting in up to 80% power enhancement. The implication of this method for COILs operating beyond the specific conditions reported here is assessed.

Direct measurements of the dissociation of I2 molecules at the optical axis of a supersonic chemical oxygen-iodine laser (COIL) as a function of I2 flow rate were carried out. This enabled us to determine the number of consumed O2(Δ1) molecules per dissociated I2 molecule. The number depends on the experimental conditions: it is 4.2±0.4 for typical conditions and I2 densities applied for the operation of the COIL, but increases at lower I2 densities. Possible dissociation mechanisms consistent with our results are discussed and the importance of dissociating I2 prior to its mixing with O2(Δ1) is stressed.

We report on a detailed parametric study of the extremely efficient supersonic chemical oxygen-iodine laser recently developed in our laboratory [V. Rybalkin, A. Katz, B. D. Barmashenko, and S. Rosenwaks, Appl. Phys. Lett. 85, 5851 (2004)]. At the early stage of operation, 40.0% efficiency was measured for 1 s followed by a sustained 35.5% chemical efficiency for 20 s. The power and spatial distributions of the gain and temperature across the flow were measured for different supersonic nozzles with both staggered and nonstaggered iodine injection holes, different injection locations along the flow and nozzle throat heights. The effects of the partial pressure of O2 and the residence time of the flow in the generator, as well as the heating of the nozzle, are discussed and shown to be crucial in attaining this high efficiency. By carefully studying and optimizing the operation of the chemical generator, 0.73 yield of singlet oxygen was obtained for conditions corresponding to the highest efficiency.