讲义5-0-波包动力学幻灯片.pptxVIP

飞秒波包动力学;OUTLINE;导论;波包动力学基本理论;外场中分子的哈密顿量 引入BO近似（绝热表象） 相应的随时间变化的分子波函数为;最终得到各个电子态之间核波函数的耦合方程（矩阵形式？）;题外话（无外场情况下）;考虑双原子分子的情况;;;;激光与分子的相互作用;;if we rewrite the state vector as then we obtain the two-state Eq.;Condon近似;;;波包的一些性质;;;In free space, U = 0, the wave-packet not only moves with speed hk/m, but also spreads.;The reason for experimental interest in Gaussian wave-packets is that they are naturally found as the ground-state wavefunction of a harmonic potential.;;if the packet finds itself in another potential of exactly the same shape, but displaced from the centre, it will simply oscillate.;However, if the potential is harmonic with a different period, the packet will breathe while moving along the classical trajectory. The breathing means that the packet changes its width as it moves about the well, but, unlike the case of dispersion, its original shape will return. If the packet is wider at the turning point than the natural ground-state wavefunction of the new harmonic well, it will become narrower than the local ground state when it is at the centre of the well ;;;it will initially oscillate in the well as it would in a harmonic potential.;However, after a time it breaks up into pieces so that it is spread about the potential surface.;A remarkable feature of the anharmonic well is that it can show revivals where the wave-packet reforms. Furthermore, fractional revivals take place where the wave-packet reforms as two (or even more) separate pieces.;波包演化的数值求解;;;Split-operator Fourier transform method;;;It is straightforward if there is only one potential surface. However, if there are two coupled surfaces we must form the exponential of a 2 x 2 matrix. diagonalize to form the exponential;;;regarded as a form of second-order expansion of the exponential operator;Homework;波包相关的物理过程;波包的产生;;;;Processes induced by chirped pulses;;Pump-probe schemes;;Wave-packet interference;;;自发辐射;;