KEYWORDS: Luminescence, Photons, Single photon, Q switched lasers, Signal processing, Light sources, Proteins, Light emitting diodes, Digital signal processing, Signal detection
A novel technique based on single photon counting is developed for tracing the non-equilibrium process by recording
the fluorescence lifetime changes over time. Different from the conventional time-correlated single photon counting
(TCSPC) method, our technique uses a 'double-time' time-correlated strategy in the single photon counting, and it can
record a sequence of fluorescence decay curves with nanosecond-scale time interval. The key point of our technique is
to assign the photons to different groups according to the relative time between photon emission and the beginning of
non-equilibrium process. It is achieved by a specially designed setup. In this setup, the instrument response function,
contributed by the photon detector and signal processing circuits, is about 250ps. The time interval between two
adjacent fluorescence decay curves is adjustable in the range of 13.5~157ns, and eight curves can be measured
simultaneously. Compared with the direct waveform recording method, our novel method can provide significantly
better accuracy in the measurement of fluorescence decay curves. An aqueous solution of tryptophan is used to
demonstrate our method with laser induced temperature-jump technique, and the possible improvements are also
discussed. The technique we introduced here has potential applications in the fields of fast biodynamic research, such
as the protein folding/unfolding kinetics.
A transient molecular probe for characterization of the surface properties of TiO2 nanoparticles in colloidal solution has been developed recently in our laboratory. The
probe molecule is all-trans-retinoic acid (ATRA) adsorbed on the TiO2 nanoparticle
surface. After photoexcitation, the photoinduced interfacial charge recombination would
generate ATRA triplet state (ATRAT) with a substantial quantum yield. While the
quantum yield of triplet ATRA generated in the solution phase is substantially low, which
renders the interfacial-charge-recombination generated triplet ATRA being a transient
probe molecule specific only to the interface. It is found that the triplet-triplet
absorption spectrum of ATRA adsorbed molecule is sensitive to its binding form with the
surface Ti atom through the carboxylic group, as well as to the polarity of the medium.
Especially the apparent lifetime of ATRAT at the TiO2 surface changes substantially when
the local polarity around the TiO2 nanoparticle changes. We found that the ATRAT
monolayer adsorbed at the TiO2 surface can be used as a transient molecular probe for the
surface binding forms, coordination state of the surface Ti atoms and the light-induced
wettability change of the TiO2 nanoparticle.
TiO2 nanoparticle, all-trans-retinoic acid, molecular probe, interfacial charge
recombination, surface binding form, light-induced wettability change.
The white-light continuum generation (WLCG) has been widely used as a probe beam for the ultrafast time-resolved difference absorbance spectrum or the seeding beam in an optical parametric amplifier (OPA). Therefore reducing the chirp effect in WLCG would be important. We report the study on WLCG in different medium by focusing 800nm laser pulse with a pulse duration of 150fs into 2mm thick CaF2, 2.4 and 0.5mm sapphire plates, try to find any medium as well as the optical pathlength effect on the chirp of the WLCG. The chirped dispersion of WLCG was determined by optical Kerr effect. The results show that the temporal span of the WLCG is almost independent on the optical pathlength of the medium in the observed spectral region, while it has an obvious dependence on the different media used.
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