Ultrafast Spectroscopic Study On Hybrid States Based On Metal Surface Plasmon Polaritons

Since the birth of quantum mechanics,with the constantly understanding of the micro-world,modern science and technology have been greatly promoted.With the continuous improvement of experimental accuracy and technical control,people began to explore the construction of some novel hybrid quantum state.The hybrid states based on surface plasmon polaritons is one kind of novel quantum state which is widely concerned.With its unique properties,it is expected to realize molecular function directional regulation and control by light filed.SPPs can be thought of as light trapped at the surface of a metal and form a strong electromagnetic field.Molecules and the enhanced electromagnetic field can interact with each other to form new hybrid states,which is reminiscent of two atomic orbitals coupling to give new molecular states.How to describe the photophysical properties of these new SPPs-molecular complex introduces new challenges to theory and experimental techniques.At present,most of the research is still focused on the construction of hybrid quantum states and steadystate measurements,few research on time-resolved spectroscopy is also limited to the typical J-aggregated molecules.Compared with the steady-state measurements,much more new structures and new phenomena will be reflected in transient spectrum measurements,which can directly reflect the nature of coherent coupling.To solve the above questions,the research of strong coupling was expanded to more abundant functional materials in this thesis.Hybrid systems formed by strong coupled SPPs and organic laser dye molecules,organic solar cells or the new perovskite materials was studied by transient absorption microspectroscopy.The formation and evolution process of the hybrid quantum states happened in the sub-picosecond and sub-nanosecond was analysed in detailed.The major research results are as the following:1.Based on the original wide-spectrum femtosecond pump-probe system in our lab,a wide-spectrum transient absorption microspectroscopy system is built.The temporal resolution of the system is kept at 100 fs,while the spatial resolution was improved to the magnitude of 10 microns,which can meet the micro size of the metal nanostructures array.2.A multimode coherent hybrid system formed by strong coupled surface plasmons in gold nanohole arrays and excitons in sulforhodamine 101 dye is investigated.A double Rabi splitting upto 255 me V and 188 me V was observed in steady-state transmission measurements.The formation of strong coupling system was confirmed from two aspects: the anticrossing energy dispersive curves and the linear relationship between the Rabi splitting energy and the square root dye molecular absorbance.More importantly,the dynamics of the multimode hybridization under double splitting was studied by transient absorption microspectroscopy.Under upper band resonance excitation,two distinctive bleaching signals corresponding to the middle and lower bands are formed,clearly fingerprint of the multimode coherent hybrid states.Furthermore,through the comparison of the kinetic evolution,we found that the low-energy coupled hybrid state can be regarded as the quasi-bound state with the lowest energy,and a long lifetime of the lower band is observed,even longer than the bleaching recovery of the uncoupled dyes.Such behavior is in perfect agreement with the non-Markovian regime.3.We demonstrate the achievement of ultrastrong coupling regime between surface plasmon modes generated by gold conical pits arrays and excitons associated to squaraine dye.A remarkable Rabi splitting up to 860 me V is measured in steadystate reflection measurements.The corresponding wavelength is 1.44 ?m,close to optical frequencies.To our knowledge,it is the largest Rabi splitting ever observed involving SPPs.Furthermore,the dynamics of the hybrid states under ultrastrong coupling regime was investigated by transient absorption microspectroscopy.It was found that the upper band cannot be determined in the TA spectra.In addition,due to the overwhelming effect due to the very fast damping of the SPP modes,the lower hybrid state shows a lifetime much shorter than the bleaching recovery of SQ dye on a flat gold film,hence providing a substantial difference with the dynamics of strongly coupled systems.4.A hybrid system formed by gold nanohole array and all inorganic Cs Pb I3 perovskite quantum dots was prepared by centrifugal deposition method.The method of centrifugal deposition overcomes the shortcomings of the traditional spin coating method,and can produce a tightly regular perovskite quantum dot film,which provides a strong guarantee for the formation of strong coupling regime.The formation of strong coupled hybrid states was further confirmed by steady-state reflection measurements.At the same time,another hybrid system consist of aluminum conical nano pits array and MAPb Ix Cl3-x perovskite film was constructed.Here,the hybrid states were formed by SPPs and free carriers,rather than the traditional molecular excitons.In order to further confirm the formation of this new type of strong coupling system,we carried out the transient absorption microspectroscopy on the hybrid system.Under resonance excitation,it is observed the presence of two distinctive bleaching signals in the transient absorption spectra which were related to the existence of the hybrid free carriers–plasmon state.Finally,our experiments on the kinetics process time decay dynamics also showed that the hybrid states have a shorter life than the bleach recovery process of the uncoupled perovskite film.