Ultrafast time-resolved fluorescence by two photon absorption excitation.

We report a time-resolved fluorescence apparatus utilizing fluorescence upconversion by noncollinear sum frequency generation and two photon absorption as an excitation. Near perfect time-resolution is achieved with 20 fs pulses to give the instrument response of 33 fs (FWHM) over the entire fluorescence wavelength for a 100 microm thick mixing crystal. Through experiments and numerical simulations, it is shown that 40 fs time-resolution can be obtained even for a 580 microm thick mixing crystal at a fluorescence wavelength longer than 500 nm.