The Investigation Of Exciton Dynamics Coupled With Phonon In MEH-PPV By Employing CARS

Time-resolved coherent anti-Stokes Raman scattering is a spectroscopy technique combined with femtosecond laser pulses that can be used to study the ultrafast dynamic processes of chemical bonds within molecules.In recent years,femtosecond CARS technology has been gradually applied to many fields of science and technology,occupying an important position in spectral measurement.The main research work of this thesis is to study and analyze the phonon relaxation kinetics of coupled excitons in polymers by femtosecond coherent anti-Stokes Raman scattering?CARS?spectroscopy.In this paper,the organic high molecular polymer MEH-PPV was selected as the research object,and the energy dissipation process of the exciton and phonon coupling in the molecular chain after MEH-PPV excitation by laser pulse was explored.MEH-PPV is a common material for making organic light-emitting devices such as light-emitting diodes.The energy dissipation process is a difficult point in our research.The dissipation method is generally divided into radiation relaxation mode and non-radiation relaxation mode.Radiation relaxation usually uses energy dissipation in the form of luminescence,and the mechanism of no-radiation relaxation requires us to lock the vibration mode?vibration relaxation is part of the non-radiative relaxation mechanism?and observe the energy of the sample after excitation.The method of dispersion is determined.We use the laser system with a pulse width of 130 fs as the light source to build the femtosecond CARS spectroscopy system.CARS is a third-order nonlinear Raman imaging modal,requiring three incident fields,including pump pulses??₁?.,Stokes pulse??₂?,detection pulse??₃?.In the experiment,we used a laser pulse with a center wavelength of 560 nm as the pump pulse(pulse width 255 cm^-1),and selected a laser pulse with a center wavelength of 600 nm as the Stokes pulse(pulse width1670 cm^-1).It can detect vibration modes in the range of 0¹925 cm^-1.The CARS signal of the organic photopolymer MEH-PPV in toluene solution was measured by femtosecond CARS spectroscopy.By adjusting the timing of the pulses,the Pump-CARS signal and the time-resolved CARS signal are obtained respectively to detect the phonon relaxation signal of the coupled excitons and the relaxation signal under the phonon coupling.By performing Fourier transform and fitting processing on the obtained data,the kinetic curves of the internal information of various molecules are obtained and analyzed,so as to grasp the energy dissipation of exciton and phonon coupling in the molecular chain of organic polymer MEH-PPV process.