Stability analysis of continuous fiber laser sustained Xe plasma

The paper employs various optical analysis methods to study the stability of continuous fiber laser sustained Xe plasma under different laser power and focusing systems. High-speed cameras were used to capture plasma images from two directions, allowing a quantitative description of the fluctuation amplitudes of the plasma centroid and diameter. Standard deviation analysis revealed that a tightly focused system and increased laser power are more favorable for improving plasma stability. High-speed photodiodes and piezoelectric film sensors were simultaneously employed to monitor changes in plasma luminous intensity and internal gas pressure, showing that the fluctuation signals of both were consistent in shape and variation. The Schlieren method revealed the presence of periodically rising thermal bubbles around the plasma. Fourier transform spectra identified a 30 Hz low frequency and several hundred Hz high frequencies in the fluctuations of the plasma centroid, diameter, and brightness, while the piezoelectric signal contained only the low frequency. Further analysis concluded that the high frequencies originate from laser power fluctuations, while the low frequencies are caused by gas convection. As the laser power increases, the frequency of the low frequency gradually decreases to a gentle level.