Luminescent instabilities in dense rare earth ion systems.

Abstract

This thesis reports experiments and theory on intrinsic mirrorless bistability in the luminescence of ytterbium-doped crystals and glasses. The main results are the observation of intrinsically bistable luminescence at room temperature and chromatic switching at low temperature, reported here for the first time. The nonlinear dynamics responsible for these optical phenomena are shown to arise from ion-ion interactions controlled by the application of resonant electromagnetic fields. On the theoretical side, the classical Lorentz local field correction is shown to be the lowest order term of radiation-driven correlation contributions to local polarization which arise from inter-ion coherences and cooperative relaxation and frequency shifts beyond the dynamic shift are predicted. The nonlinear Maxwell-Bloch equations are extended to describe energy transfer between different species of ions predicting bistability in excited state populations which then emit bistable luminescence as a consequence, and an intensity dependent transfer rate is predicted. Diffusive excitation migration in space is also explored as a possible mechanism for generating multiple instabilities, but is not predicted to give rise to hysteresis loops by itself. On the experimental side, original observations of intrinsic optical switching and hysteresis are reported in the luminescence of Yb:CsCdBr₃ and Yb, Tm:glass. Evidence of cross-coupling between different impurities is also presented, together with spectroscopic details of intrinsic chromatic switching between different luminescent transitions of the acceptor species in Yb, Er:CsCdBr₃ excited at the infrared Yb resonance wavelength. Conclusive spectroscopic evidence that excludes thermal effects as responsible for low temperature intrinsic switching is also presented. Room temperature intrinsic optical switching and hysteresis are reported for the first time in bulk Yb,Tm:glass samples. Switching, hysteresis, and clamping of laser output from waveguide channels fabricated in the glass material are also reported and indicate fundamental design limitations for compact optical amplifiers and oscillators.