By varying the output power density of a CO{sub}2 laser beam either a deep penetration or a shallow penetration welding regime can be achieved. The transition between the two regimes is accompanied by abrupt changes in the statistical and dynamical characteristics of emitted light intensity. For a characterisation of the dynamics the coarse-grained entropy rate is applied. A high entropy rate is typical for deep penetration, while a low value is characteristic for a shallow penetration welding regime. Additionally, dynamics of the welding regimes are modelled by the Langevin equation. Analysis reveals that in both welding regimes the dynamics corresponds to stochastic fluctuations around a stable fixed point. It is demonstrated that a stable node corresponds to the deep penetration welding, while a stable spiral corresponds to the shallow penetration welding. The transition between welding regimes can be thus described by a change of the fixed point character.
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