Image Processing, Based On Phase Unwrapping Of Interference Fringes Of Laser Plasma Shock Wave

The research of laser-induced plasma shock wave is an important basic theory in the field of laser application. The image processing of interferogram collected in the experiment is one of the key methods to study laser-induced plasma shock wave.In this paper, Mach-Zehnder interference is used to conduct the research of laser-induced plasma evolutionary process at first. Then, the collected interferogram is processed by Fourier transform method, frequency-domain filtering, inverse-Fourier transform method, and phase unwrapping. The algorithm of phase unwrapping is studied at last.The interferogram of laser-induced plasma shock wave is collected in real-time by the system composed by Mach-Zehnder interference system, delay device, CCD, and computer. The laser-target and air-target plasma interferograms at different delay time are obtained separately.The interferogram of laser-induced plasma shock wave is processed by programming using Fourier transform method, frequency-domain filtering, inverse Fourier transform method, and phase unwrapping. According to the interferograms whose phase are wrapped, many existing algorithms are chose to investigate the interferograms in this paper, such as Goldstein branch-cut algorithm, unweighted least-square algorithm and PCG algorithm. For the large phase step in shock wave area of the laser plasma shock wave interferogram, the interferogram can not be processed well by traditional phase unwrapping algorithm. So, on the base of classical algorithm, an algorithm whose name is "phase unwrapping algorithm based on calculating reliability of pixels" is proposed in this paper. By comparing the results with the previous algorithms, it is concluded that this algorithm is better in processing the interferogram of laser-induced plasma shock wave.The results of this paper provide a new method to investigate the physical parameters of laser-induced plasma.