Study On The Application Of Aero-Optics

In the courses of High-Energy Laser (HEL) operation, extracting beam from laser and laser beam propagation, the flow will cause laser beam quality degradation. Aero-Optics is a new subject in which the interaction between fluid motion and electromagnetic wave propagation is investigated. The aero-optical applications in laser cavity, Aero-Dynamic Windows (ADW), Beam Transport Tube (BTT) and atmosphere are studied theoretically and experimentally.By the characteristics, the aerodynamic medium can be divided into three types of ordered, random and turbulent inhomogeneities. A physical model and the evaluation factors of beam quality on laser propagation in three types of media are discussed and analyzed. The numerical models of aero-optics in HF/DF Continuous Wave Chemical Laser (CWCL) laser cavity, BTT and indoor atmosphere are set up.The relation of several definitions of beam quality in HEL technology is deduced under the supposition of small disturbance and the formula of factor (3 is also revised. From the analysis on wavefront aberration by high-speed airflow, it was pointed out that aero-optics inhomogeneity is consisted of large-scale ordered and small-scale random inhomogeneity. However, the Lateral Shear Interferometer (LSI) can realize the two kinds of measurement, and it is the better tool for aero-optical test. For ordered aberration, it is deduced and simulated that the ability of wavefront reconstruction of LSI is better than Hartmann Wavefront Sensor (HWS), for the indirect sampling information of wavefront with LSI is more than HWS. In the base of LSI, the Wavefront Prolongation Shear Interferometer (WPSI) is presented. And on the assumption of WPSI, a new algorithm of wavefront reconstruction base on wavelet transform is put forward.The flow field in 3-Slot (3S) structure HF/DF CWCL cavity is simulated numerically. The 2-dimension refractive index model is set up to simulate the inhomogeneity distributions in laser cavities. With it, the performance and beam quality in 3S and 2-Slot structure lasers are computed and analyzed. By the simulation, it is shown that the ordered aero-optical aberrations in the telescopic unstable cavity are not serious in nozzles array of 1m length. But with the increase of the length of nozzles array, it will be important, especially to over-tone HF lasers. In addition, the performance and beam quality of 3S is better than 2S.The general principle and affect on beam quality of ADW is discussed, and the aero-optical characteristics of Free-vortex Aero-Dynamic Windows (FADW) is emphasized. The inhomogeneity in a 30mmx30mm-size FADW is measured with LSI. Moreover, the one dimension wavefront aberration in output window was reconstructed and the random inhomogeneous scale distribution is given. Also, the comparison between FADW and other ADWs is made. With this method, the aero-optical inhomogeneity in a 10kW CO2 gas-dynamic-laser cavity is measured. The diagnosis shows that the cause of random inhomogeneity is ablation of nozzle throats.The atmospheric temperature rise with HEL propagation is calculated analytically and numericallyby Air Fluid Dynamics Model (AFDM). Furthermore, the thermal blooming in BTT and indoor atmosphere is simulated by AFDM. For high power laser (>100kW) with small beam size(~ 100mm) propagates in indoor air, the beam quality degradation caused by thermal blooming is estimated, and tested by experiments. Also, some methods for eliminating thermal blooming are discussed. In addition, a back-scattering model based on laser illuminating is set up and discussed. Under actual atmosphere, the model is tested.