Abstract

The dynamic spectral and temporal properties of femtosecond two-photon pumped frequency upconversion lasing in a Coumarin-500 dye solution are presented. Forward and backward lasing in a 1 cm pathlength dye solution with a concentration of 0.1 M occurs at wavelengths of 491 nm and 493.5 nm, respectively, whereas the peak wavelength of the ordinary steady-state fluorescence emission is at 513 nm. There is a real time delay of ∼2 ps between the forward pump pulse peak and the first burst of the two-photon pumped forward lasing pulse, which corresponds to the build-up time of the effective population inversion sufficient for transient lasing. In contrast, the backward output lasing pulse can involve two temporally separate components, i.e. the original backward lasing pulse as well as an additional component, due to the reflection of the forward lasing pulse from the output window. At much higher pump levels than the threshold, the output/input characteristic curve deviates from the quadratic law. The physical explanations for these experimental results are proposed.

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