An Investigation of Laser-Target Interaction Signals.

摘要

Micro distresses were created in a simulated jet engine using a pulsed ruby laser, and the electrical signals were studied at various points in the simulator. Average power levels of the target ranged from 400,000 to 4,770,000 watts per square centimeter. Target materials investigated were cold-rolled steel, Ti 64, Mn, Co, a cathode material, and high purity Fe, Ni, Ti, and Cb. It was found that the target signals have a reproductive pattern. The most general pattern observed could be separated into four regions and had the general appearance of two cycles of a sine wave. With the possible exception of the cathode material, the interpretation applied to each region was independent of the target material used. The interpretation applied to each region is: Region 1 - laser induced thermionic emission, Region 2 - plume-target interaction, Region 3 - thermionic emission of the hot flushed material, and Region 4 - oxide tail formation due to the plume-target interaction. A leading portion of Region 1 correlated with the thickness of the oxide layer on the target, and in the absence of airflow, Region 2 correlated with the depth of the hole. It was found that the blow-off from the cathode material and Ni had negative particles and produced positive pockets upon passage through the simulator. The simulator basically removed charged particles from the air stream. All other materials produced positive particles and negative pockets. It was also found that oxidation produced positive pockets. These experiments substantiate the Positive Pocket Theory proposed by Couch and suggest expanding it to include negative pockets.