An experimental and computational study of the COIL resonators for the development of the COIL thermal image marker system to the far-field objects

We have been studying the Chemical Oxygen-Iodine Laser (COIL) Thermal Image Marker System to the far field objects. This system can mark the distinguishable thermal image on the far field objects with the laser beam of the COIL to guide the Imaging Infrared homing air vehicle to the object marked thermal image with pinpoint accuracy. For the development of this system the study of the COIL resonator is the main task to meet the generation of the required high quality laser beam. Therefore, first we made two kinds of the experiments. One is to generate the distinguishable thermal image mark (TIM) on the object with stable resonator of the 13 kW output COIL system in the near field. Another is to improve the laser beam quality with the unstable resonators of the COIL system in the low gain condition. Then we studied the high power unstable resonator design for this system with the numerical simulation based on its experimental data and the two-dimensional Fresnel-Kirchhoff integration method with partially coherent scalar electric field. Finally we made the numerical far field TIM generation to verify the TIM generation with the laser beam of the studied high power unstable resonator. The result of simulation shows the fine TIM generation. The result of the experiment and the resonator design study shows that it is possible to realize the good thermal image mark, the good quality laser beam and the promising unstable resonator for the COIL Thermal Image Marker System.