Bistable chromatic switching in 648 nm laser pumped Tm-doped crystal

Intrinsic optical bistability is of great interest and has potential applications in all-optical communication. In the present work, we have extended occurrences of bistable chromatic switching to a new rare-earth-doped system, namely single Tm-doped laser crystal pumped at 648 nm avalanche wavelength. Intrinsic bistability and chromatic switching of fluorescence emission are theoretically predicted, based on the rate equation theory. By using a four-order Runge-Kutta technique, chromatic switching spectra and bistable hysteresis loop are studied numerically in detail. The numerical results show that intrinsic chromatic switching of visible-infrared spectra is achievable experimentally corresponding to the transitions of Tm ¹D ₂→³H₆ (357 nm), ¹G ₄→³H₆ (469 nm), ³H ₄-→³H₆ (787 nm), ³F ₄-→³H₆ (1716 nm), as pump power increases far beyond avalanche threshold from low power level. Furthermore, we have found that the chromatic switching appears bistable in the emission spectra for pump intensity in the vicinity of avalanche threshold. The bistable hysteresis loops of luminescence are also demonstrated numerically for the dominant emission band. Intrinsic bistable chromatic switching in Tm-doped crystal is mediated by resonant excited-state absorption up-conversion.