Analysis of penetration depth fluctuations in single-mode fibre laser welds

Penetration depth fluctuations of single-mode fibre laser welds made with long focal length optics and the effects of sinusoidal laser power modulations were studied. It was found that the welds had a high aspect ratio and were subject to spiking defects. The magnitude of the penetration fluctuations tended to be larger for deeper welds. The weld penetration profiles had positive maximal Lyapunov exponents and broadband, aperiodic power spectral densities with most of the signal power in the spectral band from 0 Hz to 1 kHz. The amplitude of the frequency response of the laser penetration to large amplitude laser power modulations decreased at rates varying from -20 to -60 dB decade-1 at modulation frequencies from 100 Hz to 1 kHz. It was found that sinusoidal laser power modulation at frequencies from 900 Hz to 3 kHz decreased the aperiodic penetration fluctuations.