Noncollinear optical parametric amplifier based femtosecond time-resolved transient fluorescence spectra: characterization and correction

Spectral distortion frequently occurs in a recently developed femtosecond time-resolved fluorescence spectroscopy based on noncollinear optical parametric amplification, which would limit its applications if it is not treated appropriately. We report the mechanism for broadening and distortion of the amplified spectrum, and it was found that the amplified fluorescence spectral width and the corresponding pulse duration were limited by the uncertainty principle. We demonstrated that the nonuniform gain curve of nonlinear optical crystal in the wide spectral region is the main cause leading to the distorted spectrum. Theoretical analysis shows that by carefully adjusting the experimental parameters, such as propagation and noncollinear angles, the spectral fidelity can be achieved in a broad region. Moreover, we also proposed a method for retrieving the genuine spectrum from the distorted amplified spectrum by experimentally measuring the gain curve encoded in the spectrum of the parametric superfluorescence, which is collected during propagation at noncollinear angles the same as those for amplified fluorescence. (C) 2009 Optical Society of America