Studies On Electronic State Vibration Modes And Their Relaxation Process With Photon Echo In Nile Blue Molecules

Along with the advent of femtosecond laser pulse, the research about three-pulsephoton echo become more and more widely. Scientists probe the liquid ultrafastdynamic process and line broadening of the electronic transition through photon echo.This paper takes Nile blue as sample, studying the three-pulse photon echo from theoryand experiment respectively.Using the optical bloch equation to calculate the bloch vectors in the process ofoptical nutation and optical free induction decay. Analysing the three-pulse photon echothrough the optical nutation and the optical free induction decay. With the Maxwellwave equation, we build the relationship between the intensity of three-pulse photonecho signal and the bloch vectors. In this paper, we treat the vibration of materialmolecules as the model of the Multimode Brownian Oscillator, and discuss that how tocalculate the three-pulse photon echo signal. Taking the Nile blue for example, we usethe model of the Multimode Brownian Oscillator to analyse the vibration of the Nileblue molecules and regard the vibration of the Nile blue molecules as the weightedcoupling result of the gaussian, overdamping, completely inhomogeneous,underdamping model. Changing the weight of these four model to alter the correlationfunction of the Nile blue molecules, we numerically simulate the three-pulse photonecho signal, the transient grating photon echo signal and the three-pulse photon echopeak shift.During the experiment research about the three-pulse photon echo of the Nile blueethanol solution, the concentration of Nile blue ethanol solution is8105mol/L, thewavelength and the pulse width of the femtosecond laser light source are623nm and40fs respectively. We divide the femtosecond laser light source into three beams and thepower of each beam pulse is20uw. On the basis of that these three femtosecond laserpulses are completely overlap both in space and time, we measure the three-pulsephoton echo signal of the Nile blue molecules by using the stepper motor to accuratelycontrol the delay time among these three femtosecond laser pulses. The accuracy of thestepper motor is13.3fs. We measure the three-pulse photon echo signal and the transientgrating photon echo signal with the lock-in amplifier to discuss the vibration model ofthe Nile blue molecules. Besides, we study the relationship between the wavelength ofthree-pulse photon echo signal and the delay time between the first pulse and the secondpulse by measuring the spectrum of transient grating photon echo signal with the fiberoptic spectrometer. Changing the wavelength of femtosecond laser light source from623nm to610nm and studying the relationship between the spectrum of transientgrating photon echo signal and the pump wavelength.