Study On Non-intrusive Aero-optical Measurement Methods And Experiments

Aero-optics related to high energy laser is widely spreaded and complicated. It is involved in the laser operation, output and propagation. The goal of aero-optical research should be to improve or avoid the laser beam quality degradation caused by aero-medium.The theory of diffraction aberrations caused by aero-medium was introduced, a physical model on laser propagation in ordered, random inhomogeneous aero-medium was discussed and analyzed. The far-field energy distributions in two condition were given. The theory of optical transportation function (OTF) in random medium field was introduced. The OTF of random medium and Strehl ratio were derived. A new method of calculating Strehl ratio was derived based on theory on spectrum analysis. The method makes use of the light deflection angles. The light deflection angle can be measured by Shack-Hartmann (S-H)sensor in experiments.In the aero-optical flow field tomography measurements, all projection data of different direction must be simultaneous. And the laser nozzle flow field up-stream and down-stream Strehl ratio simultaneous measurements have the synchronicity requirement. The working environment of high power laser is rigorous and complicated. All these factors such as synchronicity and data transporting rate were considered in the hardware matching design. Based on the consideration, a high speed line S-H sensor was designed. Several factors that influence the detecting error of S-H sensor and relevant improving methods were analyzed. The error caused by the background level of CCD camera was especially considered. It can be reduced by setting a threshold level. There is a best threshold level in practical measurement.Two different extended Strehl ratio (SR) measurement method based on line S-H sensor were introduced. The first one references the principle and methods of small aperture beam technique. The SR measurement of aero-flow medium which fit the quasi-frozen-flow assumption was analyzed. The second measurement the deflection of S-H sensor'sub-aperture wave-front, according to spectrum calculation, SR can be gotten also. This extended SR measurement method is applicable to two-dimension flow field test.The algebraic reconstruction technique (ART) was introduced. This tomographic reconstruction technique is applicable to projection data-limited cases. By the line S-H sensor mentioned in chapter 3, measurements have been made to a beam path heated by HF laser. By a high speed interferometer, tomographic measurement was made on a air column heated by electric powered wire.By means of S-H sensor with 37 lenslets, at the rate of 419Hz , the aero-optical...