Coherence Dynamics Of Chlorophyll A By Femtosecond Photon Echo

Photon echo technique is widely used for the study the ultrafast dynamical process in various substances. With the rise of femtosecond mode-locked and titanium sapphire laser, pulses with width of several femtoseconds can be experimentally obtained, which makes it possible to study the ultrafast solvent dynamics. Femtosecond photon echo technique, referred to as a useful method to the study of solvent dynamics, can measure dephasing time ranging from femtoseconds to nanoseconds, where dynamic information of vibration in the stimulated sample can be obtained via resonance excitation. Under many circumstances, the band width possesses a wider space than the vibrational level gap, so that a plurality of energy level can be simultaneously excited with the use of femtosecond photon echo. The vibrational modes in the electronically excited state can be obtained through its spectrum.Theoretically, the correlation function as model of photon echo Multimode Brownian Oscillator( MBO) is established and a simulation of time response function to incident frequency is operated, which shows that the spectral lines of the phase reconstruction are extruded along the diagonal direction and that lines of the non-phase reconstruction are extruded along the non-diagonal, and indicates that the homogeneous broadening is suppressed along the diagonal direction. The established correlation function for 5 MBO model simulates the spectrum of photon echo and peak shift of chlorophyll A molecule, and gives the result that both the variation of photon echo and peak shift spectrum, and variation of correlation function obey the same law. Simulation of temperature, pulse width, pulse type, pulse chirp influence on photon echo spectrum is conducted, which shows that the photon echo intensity has a linear relationship with temperature, an exponential relationship with pulse width and a symmetrical relationship with chirp parameter.Experimentally, the study of coherent dynamics of chlorophyll A molecule and BBO crystal(β phase Barium Boron Oxide, β-Ba B2O4) is carried out with femtosecond photon echo spectroscopy. The two-color three-pulse photon echo experiments apply the 622 nm pump light and the 800 nm probe light for the chlorophyll A methanol solution at a concentration of 5.6*10-5mol/L and the BBO crystal. The fitting parameter indicates that the rapid vibration term shares a small proportion while the slow is the main form. Three-dimensional photon echo spectrum of BBO crystal shows that the incident femtosecond pulse stimulates a single electron to the excited state. Through photon echo spectrum of chlorophyll A molecule, the decay constant for different delay time can be obtained. The fitting results shows that the rapid vibration is the main form for the initial time while the slow vibration and static perturbation is relatively weak, which is caused by the Brownian motion of chlorophyll A in solution. It can come to the conclusion that the rapid decay time of transient grating signal is about 100 fs in chloriphyll A, the slow decay time about 300 fs. The two-color three-pulse photon echo experiments show that the correlation function as MBO model can be applied for the analysis of photon echo spectroscopy.