Processing Of Laser Plasma Parameter Interferogram

Laser plasma parameter interferogram is an important information carrier for the detection of the physical parameters of laser plasma and it is an important application of optical image measurement technology in the field of plasma diagnosis. The processing of interferogram is to extract the essence of the phase information from the interferogram which can reflect the measured plasma parameters, and finally get the measured plasma parameters. Therefore, it is very important to study the reasonable and effective processing method of the interferogram of laser plasma parameter.At first, the physical principle of laser plasma interference measurement is described. And based on this principle, the laser plasma interferometry system is designed and implemented. The system records the interferogram of laser plasma parameter.Then, the phase extraction method of interferogram is studied from two ways of the spatial domain image processing and the frequency domain image processing. In the research of phase extraction of interferogram based on spatial processing, the classical fringe offset method is studied. The processing steps of this method are realized, such as image preprocessing, binarization, fringe thinning and so on. And in view of the possible flaws in the fringe thinning process, the method of repairing the single pixel width fringes is designed. The complete offset information of the interference fringes and the corresponding phase values are extracted from the original interferogram by the method. In the research of phase extraction of interferogram based on frequency domain processing, the traditional phase extraction method based on Fourier transform is studied and realized. Considering the single interference image is sensitive to system error or phase noise in the process of phase extraction, the improved phase extraction method based on Fourier transform and double interferogram is proposed. to reduce the phase error caused by noise or system error, and to improve the accuracy of phase extraction. Because the phase results from the frequency domain processing method are non continuous wrapped phase, it cannot be directly applied to the subsequent parameter solution; the phase unwrapping algorithm is studied. And two classical phase unwrapping algorithms are implemented, the quality map guidance method and the least square method, In order to solve the problem that the two phase unwrapping algorithms cannot satisfy requirements to accuracy and phase continuity, an improved phase unwrapping algorithm is proposed, which is based on the combination of the quality map guidance and data fitting. This improved phase unwrapping algorithm adopts a divide and rule strategy, both to ensure accuracy, and effectively improve the continuity of unwrapping phase.Finally, based on the phase distribution map obtained from the image processing, the Abel inverse transform of the continuous phase distribution information is completed, the spatial distributions of the electron density of the laser plasma corresponding to each interferogram are solved.