Ultrafast time-resolved fluorescence at cryogenic temperature

Time resolved fluorescence at low temperature can be a powerful tool for the study of dynamics and spectroscopy. We have developed a time resolved fluorescence apparatus that provides a time resolution of 45 fs at cryogenic temperature, which is comparable to the best time resolution at ambient temperature. A continuous flow cryostat with a customized vacuum shroud and fluorescence upconversion gating by sum frequency generation were employed. A reflective Cassegrain type microscope objective lens was used to collect and to image the fluorescence to achieve high time resolution. It was demonstrated that time-resolved fluorescence spectra can also be measured directly without the spectra reconstruction at the same time resolution by in situ adjustment of the time delay to compensate the group velocity dispersion. Heat dissipation of the sample holder and the actual temperature of the irradiated volume were estimated by measuring the steady-state emission spectra of prodan solution in two different sample thicknesses, which provides a design consideration for the sample cell. The time-resolved fluorescence spectra of prodan, which undergoes charge transfer in the excited state, were measured at low temperature to demonstrate the capability of the apparatus. Published by AIP Publishing.11Nsciescopu