Selective control of excitation pathways of upconverted fluorescent states using a broadband laser and a spectral mask

We present a new technique to study materials' response to broadband, optical excitation using upconversion through excited state absorption. We use the broadband spectrum from an ultrafast laser coupled to a spectral shaper to manipulate our excitation bandwidth and selectively control which transitions occur in the ground state and excited state absorptions. By analyzing the effects of spectral shaping of the excitation laser on the emission yield of fluorescent light, we can test models of the electron population densities and transition probabilities to recover electron energy-level-specific information about the system being studied. Here, we apply this technique to Y sub(2)O sub(3):Er super(3 +).