(Color online) Setup used in the pump and probe experiments.
(Color online) Room temperature absorption coefficient of the 2.5 mol % Ho3+ doped glass ceramic sample (black solid line) and excitation spectrum of the upconversion emission band under detection at 545 nm (red dashed line).
Stimulated cross sections of the transitions from the 5 F 3, 5 S 2: 5 F 4, and 5 F 5 levels to the ground state.
(Color online) Comparison of the UC emission spectra of Ho3+ ions under pump at 750 nm (black solid lines) and pump and probe (color solid lines) excitation conditions when the probe wavelength is tuned at (a) 488 nm, (b) 545 nm, and (c) 650 nm. The spectra have been shifted for clarity. The probe profile is given at the bottom of each spectrum.
(Color online) Scheme of the photon avalanche UC mechanism.
(Color online) Net gain coefficient as a function of the pump power density measured at (a) 488 nm; (b) 545 nm; and (c) 650 nm.
Experimental (f expt) and calculated (f calc) oscillator strengths obtained in an oxyfluoride GC samples doped with 2.5 mol % of Ho3+. All transitions are from the 5 I 8 state to the indicated levels.
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