Ultrasensitive femtosecond time-resolved fluorescence spectroscopy for relaxation processes by using parametric amplification

We report the gain factor, detection limit, and linearity of a femtosecond time-resolved spectrometer for ultraweak fluorescence based on a 400 nm pumped femtosecond noncollinear optical parametric amplifier. By employing the parametric fluorescence amplifier, the time-resolved fluorescence spectra of Rhodamine 6G dye in ethanol was measured. It is proved that a good spectral fidelity has been achieved in the measurement of fluorescence spectra with this technique. The measured gain factor of this parametric fluorescence amplifier is found to be ∼1.2×106, and the detection limit is 5.1 aJ per pulse, corresponding to 15 fluorescence photons at 580 nm. With this technique, we have acquired the transient fluorescence spectra as well as the fluorescence decay profile of CdSxSe1−x(x=0.78) nanobelts. Our results demonstrate the feasibility of this technique as an ultrasensitive time-resolved fluorescence spectrometer.