Holographic visualization of the mixed gas in COIL

The chemical oxygen iodine laser (COIL) is an efficient source of high power with excellent beam quality and flexibility in beam delivery through an optical fiber. The understanding of density distribution of the gas flow in a COIL is important because the uniform gas flow is required for uniform laser output. The knowledge in the density distribution show the profile of the pressure and the temperature. Many optical methods such as shadowgraphy, schlieren, Mach-Zehnder interferometer have been applied to visualize the density distribution of mixed gas in various fields, but the visualization of gas flow in a COIL has never been investigated. The measurement of density distribution by the interferometric visualization has the advantage of quantitative analysis and high sensitivity. In the paper, the gas flow in a COIL was visualized with a real-time holographic interferometer and recorded with a high-speed camera under an environment with some vibration. The interference fringe patterns induced by the variations in the refractive index of gas were measured both in the iodine mixing region and in the laser gain region.