Type-I intermittency route to chaos in passively Q-switched Tm:YLF laser emitting at 2.3 μm

\nWe report on an original chaotic dynamic behaviour of a passively Q-switched 2.3-μm Thulium laser operating on the 3H4 → 3H5 transition. The experiment employs a Tm:LiYF4 laser crystal within various laser cavity configurations, involving optional additional cascade laser operation on the 3F4 → 3H6 transition at 1.9 μm. The saturable absorber employed is Cr2+:ZnSe, which is exclusively saturated by the 2.3 μm laser emission. A precise analysis of the Q-switching dynamics shows a pronounced inclination of the cascade laser scheme towards chaotic operation. To investigate the origins of chaos, we originally monitor the metastable 3F4 level population using cascade laser operation at 1.9 μm, which proves to be a crucial underlying parameter for explaining the observed instabilities. This analysis allows for explaining the specific dynamics of the Q-switched 2.3 μm Tm-laser intrinsically linked to Tm3+-doped materials. A very atypical route to chaos for a Q-switched laser is demonstrated involving type I intermittencies. The obtained results are of great interest for studying the premises of chaos in pulsed solid-state lasers.\n